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 $225.97   6.692%   $241.0919   $241.09   $241.10   $241.10  
  Purchase #2 $64.90   5.314%   $68.3488   $68.35   $68.35   $68.30  
  Purchase #3 $161.94   6.164%   $171.922   $171.92   $171.90   $171.90  
  Purchase #4 $39.37   7.509%   $42.3263   $42.33   $42.35   $42.30  
  Purchase #5 $203.62   3.467%   $210.6795   $210.68   $210.70   $210.70  
  Purchase #6 $64.46   6.262%   $68.4965   $68.50   $68.50   $68.50  
  Purchase #7 $118.44   4.369%   $123.6146   $123.61   $123.60   $123.60  
  7 purchase totals = $878.70       $926.4796   $926.48   $926.50   $926.40