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 $32.55   7.343%   $34.9401   $34.94   $34.95   $34.90  
  Purchase #2 $126.25   7.220%   $135.3653   $135.37   $135.35   $135.40  
  Purchase #3 $141.81   8.565%   $153.956   $153.96   $153.95   $154.00  
  Purchase #4 $44.61   9.662%   $48.9202   $48.92   $48.90   $48.90  
  Purchase #5 $200.55   11.109%   $222.8291   $222.83   $222.85   $222.80  
  Purchase #6 $11.34   10.197%   $12.4963   $12.50   $12.50   $12.50  
  Purchase #7 $103.74   9.424%   $113.5165   $113.52   $113.50   $113.50  
  7 purchase totals = $660.85       $722.0235   $722.04   $722.00   $722.00