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 $61.42   3.239%   $63.4094   $63.41   $63.40   $63.40  
  Purchase #2 $63.94   3.503%   $66.1798   $66.18   $66.20   $66.20  
  Purchase #3 $48.92   11.459%   $54.5257   $54.53   $54.55   $54.50  
  Purchase #4 $166.59   13.468%   $189.0263   $189.03   $189.05   $189.00  
  Purchase #5 $139.46   5.533%   $147.1763   $147.18   $147.20   $147.20  
  Purchase #6 $205.69   3.277%   $212.4305   $212.43   $212.45   $212.40  
  Purchase #7 $179.33   8.133%   $193.9149   $193.91   $193.90   $193.90  
  7 purchase totals = $865.35       $926.6629   $926.67   $926.75   $926.60