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 $45.77   5.858%   $48.4512   $48.45   $48.45   $48.50  
  Purchase #2 $214.76   11.441%   $239.3307   $239.33   $239.35   $239.30  
  Purchase #3 $194.42   3.363%   $200.9583   $200.96   $200.95   $201.00  
  Purchase #4 $139.91   12.612%   $157.5554   $157.56   $157.55   $157.60  
  Purchase #5 $191.66   12.776%   $216.1465   $216.15   $216.15   $216.10  
  Purchase #6 $160.90   4.592%   $168.2885   $168.29   $168.30   $168.30  
  Purchase #7 $17.66   7.679%   $19.0161   $19.02   $19.00   $19.00  
  7 purchase totals = $965.08       $1,049.7467   $1,049.76   $1,049.75   $1,049.80