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 $234.25   11.850%   $262.0086   $262.01   $262.00   $262.00  
  Purchase #2 $50.80   6.511%   $54.1076   $54.11   $54.10   $54.10  
  Purchase #3 $16.44   5.508%   $17.3455   $17.35   $17.35   $17.30  
  Purchase #4 $121.51   6.808%   $129.7824   $129.78   $129.80   $129.80  
  Purchase #5 $120.41   12.623%   $135.6094   $135.61   $135.60   $135.60  
  Purchase #6 $36.53   12.858%   $41.227   $41.23   $41.25   $41.20  
  Purchase #7 $51.79   10.453%   $57.2036   $57.20   $57.20   $57.20  
  7 purchase totals = $631.73       $697.2841   $697.29   $697.30   $697.20