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 $96.31   6.147%   $102.2302   $102.23   $102.25   $102.20  
  Purchase #2 $114.29   6.389%   $121.592   $121.59   $121.60   $121.60  
  Purchase #3 $212.95   7.802%   $229.5644   $229.56   $229.55   $229.60  
  Purchase #4 $64.64   5.431%   $68.1506   $68.15   $68.15   $68.20  
  Purchase #5 $184.53   13.609%   $209.6427   $209.64   $209.65   $209.60  
  Purchase #6 $163.54   12.203%   $183.4968   $183.50   $183.50   $183.50  
  Purchase #7 $88.94   13.808%   $101.2208   $101.22   $101.20   $101.20  
  7 purchase totals = $925.20       $1,015.8975   $1,015.89   $1,015.90   $1,015.90