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 $155.31   11.482%   $173.1427   $173.14   $173.15   $173.10  
  Purchase #2 $200.80   10.605%   $222.0948   $222.09   $222.10   $222.10  
  Purchase #3 $26.44   9.619%   $28.9833   $28.98   $29.00   $29.00  
  Purchase #4 $7.57   5.477%   $7.9846   $7.98   $8.00   $8.00  
  Purchase #5 $28.38   10.517%   $31.3647   $31.36   $31.35   $31.40  
  Purchase #6 $101.53   6.617%   $108.2482   $108.25   $108.25   $108.20  
  Purchase #7 $221.57   10.863%   $245.6391   $245.64   $245.65   $245.60  
  7 purchase totals = $741.60       $817.4574   $817.44   $817.50   $817.40