Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $241.35   12.454%   $271.4077   $271.41   $271.40   $271.40  
  Purchase #2 $236.46   11.365%   $263.3337   $263.33   $263.35   $263.30  
  Purchase #3 $132.31   12.254%   $148.5233   $148.52   $148.50   $148.50  
  Purchase #4 $216.62   11.575%   $241.6938   $241.69   $241.70   $241.70  
  Purchase #5 $90.29   4.797%   $94.6212   $94.62   $94.60   $94.60  
  Purchase #6 $176.77   9.573%   $193.6922   $193.69   $193.70   $193.70  
  Purchase #7 $242.94   11.557%   $271.0166   $271.02   $271.00   $271.00  
  7 purchase totals = $1,336.74       $1,484.2885   $1,484.28   $1,484.25   $1,484.20