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 $215.56   10.414%   $238.0084   $238.01   $238.00   $238.00  
  Purchase #2 $128.61   6.159%   $136.5311   $136.53   $136.55   $136.50  
  Purchase #3 $110.95   5.802%   $117.3873   $117.39   $117.40   $117.40  
  Purchase #4 $248.80   10.552%   $275.0534   $275.05   $275.05   $275.10  
  Purchase #5 $83.43   13.454%   $94.6547   $94.65   $94.65   $94.70  
  Purchase #6 $203.50   13.110%   $230.1789   $230.18   $230.20   $230.20  
  Purchase #7 $59.33   10.494%   $65.5561   $65.56   $65.55   $65.60  
  7 purchase totals = $1,050.18       $1,157.3699   $1,157.37   $1,157.40   $1,157.50