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 $58.91   10.376%   $65.0225   $65.02   $65.00   $65.00  
  Purchase #2 $195.87   7.815%   $211.1772   $211.18   $211.20   $211.20  
  Purchase #3 $179.80   8.626%   $195.3095   $195.31   $195.30   $195.30  
  Purchase #4 $52.31   3.434%   $54.1063   $54.11   $54.10   $54.10  
  Purchase #5 $27.58   6.632%   $29.4091   $29.41   $29.40   $29.40  
  Purchase #6 $140.86   5.489%   $148.5918   $148.59   $148.60   $148.60  
  Purchase #7 $24.70   3.251%   $25.503   $25.50   $25.50   $25.50  
  7 purchase totals = $680.03       $729.1194   $729.12   $729.10   $729.10