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 $39.41   6.172%   $41.8424   $41.84   $41.85   $41.80  
  Purchase #2 $231.33   11.538%   $258.0209   $258.02   $258.00   $258.00  
  Purchase #3 $109.27   9.140%   $119.2573   $119.26   $119.25   $119.30  
  Purchase #4 $167.50   3.710%   $173.7143   $173.71   $173.70   $173.70  
  Purchase #5 $231.78   6.299%   $246.3798   $246.38   $246.40   $246.40  
  Purchase #6 $152.63   4.284%   $159.1687   $159.17   $159.15   $159.20  
  Purchase #7 $193.52   5.111%   $203.4108   $203.41   $203.40   $203.40  
  7 purchase totals = $1,125.44       $1,201.7942   $1,201.79   $1,201.75   $1,201.80