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 $62.58   5.548%   $66.0519   $66.05   $66.05   $66.10  
  Purchase #2 $38.86   4.829%   $40.7365   $40.74   $40.75   $40.70  
  Purchase #3 $88.48   4.862%   $92.7819   $92.78   $92.80   $92.80  
  Purchase #4 $175.93   12.323%   $197.6099   $197.61   $197.60   $197.60  
  Purchase #5 $190.42   11.855%   $212.9943   $212.99   $213.00   $213.00  
  Purchase #6 $110.28   6.106%   $117.0137   $117.01   $117.00   $117.00  
  Purchase #7 $44.33   9.459%   $48.5232   $48.52   $48.50   $48.50  
  7 purchase totals = $710.88       $775.7114   $775.70   $775.70   $775.70