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 $68.97   8.521%   $74.8469   $74.85   $74.85   $74.80  
  Purchase #2 $134.72   13.270%   $152.5973   $152.60   $152.60   $152.60  
  Purchase #3 $41.79   13.177%   $47.2967   $47.30   $47.30   $47.30  
  Purchase #4 $136.50   5.306%   $143.7427   $143.74   $143.75   $143.70  
  Purchase #5 $120.95   9.118%   $131.9782   $131.98   $132.00   $132.00  
  Purchase #6 $200.93   6.156%   $213.2993   $213.30   $213.30   $213.30  
  Purchase #7 $60.47   4.117%   $62.9595   $62.96   $62.95   $63.00  
  7 purchase totals = $764.33       $826.7206   $826.73   $826.75   $826.70