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 $63.43   12.797%   $71.5471   $71.55   $71.55   $71.50  
  Purchase #2 $137.43   3.828%   $142.6908   $142.69   $142.70   $142.70  
  Purchase #3 $126.68   6.815%   $135.3132   $135.31   $135.30   $135.30  
  Purchase #4 $246.39   12.136%   $276.2919   $276.29   $276.30   $276.30  
  Purchase #5 $77.51   9.525%   $84.8928   $84.89   $84.90   $84.90  
  Purchase #6 $205.85   8.820%   $224.006   $224.01   $224.00   $224.00  
  Purchase #7 $13.82   7.867%   $14.9072   $14.91   $14.90   $14.90  
  7 purchase totals = $871.11       $949.6490   $949.65   $949.65   $949.60