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 $34.44   8.294%   $37.2965   $37.30   $37.30   $37.30  
  Purchase #2 $91.58   11.563%   $102.1694   $102.17   $102.15   $102.20  
  Purchase #3 $23.87   5.819%   $25.259   $25.26   $25.25   $25.30  
  Purchase #4 $245.95   5.869%   $260.3848   $260.38   $260.40   $260.40  
  Purchase #5 $191.39   6.220%   $203.2945   $203.29   $203.30   $203.30  
  Purchase #6 $65.93   6.416%   $70.1601   $70.16   $70.15   $70.20  
  Purchase #7 $166.54   6.187%   $176.8438   $176.84   $176.85   $176.80  
  7 purchase totals = $819.70       $875.4081   $875.40   $875.40   $875.50