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 $54.50   13.279%   $61.7371   $61.74   $61.75   $61.70  
  Purchase #2 $77.76   10.333%   $85.7949   $85.79   $85.80   $85.80  
  Purchase #3 $26.46   8.669%   $28.7538   $28.75   $28.75   $28.80  
  Purchase #4 $221.94   10.861%   $246.0449   $246.04   $246.05   $246.00  
  Purchase #5 $197.30   7.585%   $212.2652   $212.27   $212.25   $212.30  
  Purchase #6 $177.86   9.799%   $195.2885   $195.29   $195.30   $195.30  
  Purchase #7 $183.84   11.754%   $205.4486   $205.45   $205.45   $205.40  
  7 purchase totals = $939.66       $1,035.3330   $1,035.33   $1,035.35   $1,035.30