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 $169.34   11.614%   $189.0071   $189.01   $189.00   $189.00  
  Purchase #2 $117.63   7.158%   $126.05   $126.05   $126.05   $126.10  
  Purchase #3 $135.69   5.401%   $143.0186   $143.02   $143.00   $143.00  
  Purchase #4 $62.30   6.352%   $66.2573   $66.26   $66.25   $66.30  
  Purchase #5 $236.69   6.228%   $251.4311   $251.43   $251.45   $251.40  
  Purchase #6 $181.96   10.662%   $201.3606   $201.36   $201.35   $201.40  
  Purchase #7 $159.91   9.113%   $174.4826   $174.48   $174.50   $174.50  
  7 purchase totals = $1,063.52       $1,151.6073   $1,151.61   $1,151.60   $1,151.70