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 $20.28   13.289%   $22.975   $22.98   $23.00   $23.00  
  Purchase #2 $150.36   4.471%   $157.0826   $157.08   $157.10   $157.10  
  Purchase #3 $75.76   8.685%   $82.3398   $82.34   $82.35   $82.30  
  Purchase #4 $15.94   13.432%   $18.0811   $18.08   $18.10   $18.10  
  Purchase #5 $112.63   7.715%   $121.3194   $121.32   $121.30   $121.30  
  Purchase #6 $71.92   13.714%   $81.7831   $81.78   $81.80   $81.80  
  Purchase #7 $39.88   13.717%   $45.3503   $45.35   $45.35   $45.40  
  7 purchase totals = $486.77       $528.9313   $528.93   $529.00   $529.00