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 $182.51   13.709%   $207.5303   $207.53   $207.55   $207.50  
  Purchase #2 $36.36   11.249%   $40.4501   $40.45   $40.45   $40.50  
  Purchase #3 $101.54   5.203%   $106.8231   $106.82   $106.80   $106.80  
  Purchase #4 $107.90   10.285%   $118.9975   $119.00   $119.00   $119.00  
  Purchase #5 $232.37   10.462%   $256.6805   $256.68   $256.70   $256.70  
  Purchase #6 $183.28   10.102%   $201.7949   $201.79   $201.80   $201.80  
  Purchase #7 $186.56   13.363%   $211.49   $211.49   $211.50   $211.50  
  7 purchase totals = $1,030.52       $1,143.7664   $1,143.76   $1,143.80   $1,143.80