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 $39.55   12.344%   $44.4321   $44.43   $44.45   $44.40  
  Purchase #2 $240.80   6.549%   $256.57   $256.57   $256.55   $256.60  
  Purchase #3 $46.37   11.494%   $51.6998   $51.70   $51.70   $51.70  
  Purchase #4 $245.83   7.404%   $264.0313   $264.03   $264.05   $264.00  
  Purchase #5 $85.34   12.676%   $96.1577   $96.16   $96.15   $96.20  
  Purchase #6 $27.27   8.702%   $29.643   $29.64   $29.65   $29.60  
  Purchase #7 $17.85   6.387%   $18.9901   $18.99   $19.00   $19.00  
  7 purchase totals = $703.01       $761.5240   $761.52   $761.55   $761.50