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 $201.48   13.452%   $228.5831   $228.58   $228.60   $228.60  
  Purchase #2 $210.78   3.260%   $217.6514   $217.65   $217.65   $217.70  
  Purchase #3 $140.64   7.208%   $150.7773   $150.78   $150.80   $150.80  
  Purchase #4 $120.32   11.220%   $133.8199   $133.82   $133.80   $133.80  
  Purchase #5 $84.50   3.167%   $87.1761   $87.18   $87.20   $87.20  
  Purchase #6 $232.58   5.707%   $245.8533   $245.85   $245.85   $245.90  
  Purchase #7 $159.98   6.699%   $170.6971   $170.70   $170.70   $170.70  
  7 purchase totals = $1,150.28       $1,234.5582   $1,234.56   $1,234.60   $1,234.70