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 $227.78   13.791%   $259.1931   $259.19   $259.20   $259.20  
  Purchase #2 $125.60   12.220%   $140.9483   $140.95   $140.95   $140.90  
  Purchase #3 $179.81   11.764%   $200.9628   $200.96   $200.95   $201.00  
  Purchase #4 $20.68   6.586%   $22.042   $22.04   $22.05   $22.00  
  Purchase #5 $94.41   10.335%   $104.1673   $104.17   $104.15   $104.20  
  Purchase #6 $213.50   12.179%   $239.5022   $239.50   $239.50   $239.50  
  Purchase #7 $54.30   7.459%   $58.3502   $58.35   $58.35   $58.40  
  7 purchase totals = $916.08       $1,025.1659   $1,025.16   $1,025.15   $1,025.20