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 $177.30   8.323%   $192.0567   $192.06   $192.05   $192.10  
  Purchase #2 $201.87   9.383%   $220.8115   $220.81   $220.80   $220.80  
  Purchase #3 $87.42   5.388%   $92.1302   $92.13   $92.15   $92.10  
  Purchase #4 $141.76   11.507%   $158.0723   $158.07   $158.05   $158.10  
  Purchase #5 $204.43   4.496%   $213.6212   $213.62   $213.60   $213.60  
  Purchase #6 $236.64   10.136%   $260.6258   $260.63   $260.65   $260.60  
  Purchase #7 $137.39   5.365%   $144.761   $144.76   $144.75   $144.80  
  7 purchase totals = $1,186.81       $1,282.0787   $1,282.08   $1,282.05   $1,282.10