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 $210.84   11.801%   $235.7212   $235.72   $235.70   $235.70  
  Purchase #2 $206.35   5.136%   $216.9481   $216.95   $216.95   $216.90  
  Purchase #3 $69.68   7.759%   $75.0865   $75.09   $75.10   $75.10  
  Purchase #4 $34.91   3.313%   $36.0666   $36.07   $36.05   $36.10  
  Purchase #5 $165.84   7.617%   $178.472   $178.47   $178.45   $178.50  
  Purchase #6 $111.67   13.102%   $126.301   $126.30   $126.30   $126.30  
  Purchase #7 $29.50   12.421%   $33.1642   $33.16   $33.15   $33.20  
  7 purchase totals = $828.79       $901.7596   $901.76   $901.70   $901.80