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 $59.59   3.474%   $61.6602   $61.66   $61.65   $61.70  
  Purchase #2 $17.53   9.763%   $19.2415   $19.24   $19.25   $19.20  
  Purchase #3 $74.25   13.180%   $84.0362   $84.04   $84.05   $84.00  
  Purchase #4 $128.44   13.658%   $145.9823   $145.98   $146.00   $146.00  
  Purchase #5 $187.94   13.350%   $213.03   $213.03   $213.05   $213.00  
  Purchase #6 $250.33   5.570%   $264.2734   $264.27   $264.25   $264.30  
  Purchase #7 $80.56   10.208%   $88.7836   $88.78   $88.80   $88.80  
  7 purchase totals = $798.64       $877.0072   $877.00   $877.05   $877.00