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 $50.68   7.606%   $54.5347   $54.53   $54.55   $54.50  
  Purchase #2 $176.26   11.177%   $195.9606   $195.96   $195.95   $196.00  
  Purchase #3 $35.50   5.840%   $37.5732   $37.57   $37.55   $37.60  
  Purchase #4 $165.55   4.637%   $173.2266   $173.23   $173.25   $173.20  
  Purchase #5 $39.98   10.714%   $44.2635   $44.26   $44.25   $44.30  
  Purchase #6 $198.31   7.774%   $213.7266   $213.73   $213.75   $213.70  
  Purchase #7 $113.31   11.753%   $126.6273   $126.63   $126.65   $126.60  
  7 purchase totals = $779.59       $845.9125   $845.91   $845.95   $845.90