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 $50.98   7.794%   $54.9534   $54.95   $54.95   $55.00  
  Purchase #2 $84.97   12.560%   $95.6422   $95.64   $95.65   $95.60  
  Purchase #3 $82.43   4.313%   $85.9852   $85.99   $86.00   $86.00  
  Purchase #4 $220.61   7.717%   $237.6345   $237.63   $237.65   $237.60  
  Purchase #5 $178.74   7.304%   $191.7952   $191.80   $191.80   $191.80  
  Purchase #6 $118.70   6.855%   $126.8369   $126.84   $126.85   $126.80  
  Purchase #7 $50.90   11.792%   $56.9021   $56.90   $56.90   $56.90  
  7 purchase totals = $787.33       $849.7495   $849.75   $849.80   $849.70