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 $213.35   11.802%   $238.5296   $238.53   $238.55   $238.50  
  Purchase #2 $155.43   13.615%   $176.5918   $176.59   $176.60   $176.60  
  Purchase #3 $151.63   12.290%   $170.2653   $170.27   $170.25   $170.30  
  Purchase #4 $181.60   3.282%   $187.5601   $187.56   $187.55   $187.60  
  Purchase #5 $41.94   6.251%   $44.5617   $44.56   $44.55   $44.60  
  Purchase #6 $180.64   9.740%   $198.2343   $198.23   $198.25   $198.20  
  Purchase #7 $230.57   12.403%   $259.1676   $259.17   $259.15   $259.20  
  7 purchase totals = $1,155.16       $1,274.9104   $1,274.91   $1,274.90   $1,275.00