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 $105.95   9.591%   $116.1117   $116.11   $116.10   $116.10  
  Purchase #2 $206.30   13.639%   $234.4373   $234.44   $234.45   $234.40  
  Purchase #3 $46.53   5.466%   $49.0733   $49.07   $49.05   $49.10  
  Purchase #4 $112.75   7.364%   $121.0529   $121.05   $121.05   $121.10  
  Purchase #5 $120.55   3.478%   $124.7427   $124.74   $124.75   $124.70  
  Purchase #6 $210.87   10.310%   $232.6107   $232.61   $232.60   $232.60  
  Purchase #7 $131.82   11.391%   $146.8356   $146.84   $146.85   $146.80  
  7 purchase totals = $934.77       $1,024.8642   $1,024.86   $1,024.85   $1,024.80