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 $241.98   12.721%   $272.7623   $272.76   $272.75   $272.80  
  Purchase #2 $87.26   5.320%   $91.9022   $91.90   $91.90   $91.90  
  Purchase #3 $62.99   3.699%   $65.32   $65.32   $65.30   $65.30  
  Purchase #4 $42.51   3.829%   $44.1377   $44.14   $44.15   $44.10  
  Purchase #5 $212.26   5.685%   $224.327   $224.33   $224.35   $224.30  
  Purchase #6 $140.87   9.470%   $154.2104   $154.21   $154.20   $154.20  
  Purchase #7 $105.47   5.139%   $110.8901   $110.89   $110.90   $110.90  
  7 purchase totals = $893.34       $963.5497   $963.55   $963.55   $963.50