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 $72.37   5.755%   $76.5349   $76.53   $76.55   $76.50  
  Purchase #2 $71.73   7.178%   $76.8788   $76.88   $76.90   $76.90  
  Purchase #3 $153.60   5.131%   $161.4812   $161.48   $161.50   $161.50  
  Purchase #4 $76.84   13.791%   $87.437   $87.44   $87.45   $87.40  
  Purchase #5 $28.61   3.277%   $29.5475   $29.55   $29.55   $29.50  
  Purchase #6 $242.93   6.160%   $257.8945   $257.89   $257.90   $257.90  
  Purchase #7 $213.93   12.570%   $240.821   $240.82   $240.80   $240.80  
  7 purchase totals = $860.01       $930.5949   $930.59   $930.65   $930.50