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 $32.98   5.836%   $34.9047   $34.90   $34.90   $34.90  
  Purchase #2 $120.28   3.731%   $124.7676   $124.77   $124.75   $124.80  
  Purchase #3 $247.96   3.286%   $256.108   $256.11   $256.10   $256.10  
  Purchase #4 $78.97   11.292%   $87.8873   $87.89   $87.90   $87.90  
  Purchase #5 $52.95   3.233%   $54.6619   $54.66   $54.65   $54.70  
  Purchase #6 $5.56   7.229%   $5.9619   $5.96   $5.95   $6.00  
  Purchase #7 $141.91   6.148%   $150.6346   $150.63   $150.65   $150.60  
  7 purchase totals = $680.61       $714.9260   $714.92   $714.90   $715.00