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 $234.84   4.781%   $246.0677   $246.07   $246.05   $246.10  
  Purchase #2 $147.75   8.556%   $160.3915   $160.39   $160.40   $160.40  
  Purchase #3 $88.52   6.489%   $94.2641   $94.26   $94.25   $94.30  
  Purchase #4 $207.83   13.439%   $235.7603   $235.76   $235.75   $235.80  
  Purchase #5 $250.43   11.690%   $279.7053   $279.71   $279.70   $279.70  
  Purchase #6 $194.40   9.226%   $212.3353   $212.34   $212.35   $212.30  
  Purchase #7 $150.76   10.332%   $166.3365   $166.34   $166.35   $166.30  
  7 purchase totals = $1,274.53       $1,394.8607   $1,394.87   $1,394.85   $1,394.90