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 $85.38   12.495%   $96.0482   $96.05   $96.05   $96.00  
  Purchase #2 $63.29   7.735%   $68.1855   $68.19   $68.20   $68.20  
  Purchase #3 $84.26   5.178%   $88.623   $88.62   $88.60   $88.60  
  Purchase #4 $46.31   9.120%   $50.5335   $50.53   $50.55   $50.50  
  Purchase #5 $66.50   4.537%   $69.5171   $69.52   $69.50   $69.50  
  Purchase #6 $198.57   8.814%   $216.072   $216.07   $216.05   $216.10  
  Purchase #7 $79.48   11.265%   $88.4334   $88.43   $88.45   $88.40  
  7 purchase totals = $623.79       $677.4127   $677.41   $677.40   $677.30