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 $126.30   6.358%   $134.3302   $134.33   $134.35   $134.30  
  Purchase #2 $63.49   9.134%   $69.2892   $69.29   $69.30   $69.30  
  Purchase #3 $62.43   11.679%   $69.7212   $69.72   $69.70   $69.70  
  Purchase #4 $85.97   6.776%   $91.7953   $91.80   $91.80   $91.80  
  Purchase #5 $34.42   4.573%   $35.994   $35.99   $36.00   $36.00  
  Purchase #6 $242.41   13.282%   $274.6069   $274.61   $274.60   $274.60  
  Purchase #7 $75.56   11.808%   $84.4821   $84.48   $84.50   $84.50  
  7 purchase totals = $690.58       $760.2189   $760.22   $760.25   $760.20