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 $227.57   6.719%   $242.8604   $242.86   $242.85   $242.90  
  Purchase #2 $163.28   11.848%   $182.6254   $182.63   $182.65   $182.60  
  Purchase #3 $100.65   3.699%   $104.373   $104.37   $104.35   $104.40  
  Purchase #4 $60.85   12.170%   $68.2554   $68.26   $68.25   $68.30  
  Purchase #5 $156.69   10.765%   $173.5577   $173.56   $173.55   $173.60  
  Purchase #6 $205.49   11.400%   $228.9159   $228.92   $228.90   $228.90  
  Purchase #7 $138.82   10.353%   $153.192   $153.19   $153.20   $153.20  
  7 purchase totals = $1,053.35       $1,153.7798   $1,153.79   $1,153.75   $1,153.90