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 $54.37   12.449%   $61.1385   $61.14   $61.15   $61.10  
  Purchase #2 $234.98   4.727%   $246.0875   $246.09   $246.10   $246.10  
  Purchase #3 $60.44   13.559%   $68.6351   $68.64   $68.65   $68.60  
  Purchase #4 $9.96   4.597%   $10.4179   $10.42   $10.40   $10.40  
  Purchase #5 $236.79   9.490%   $259.2614   $259.26   $259.25   $259.30  
  Purchase #6 $65.64   13.292%   $74.3649   $74.36   $74.35   $74.40  
  Purchase #7 $243.72   12.487%   $274.1533   $274.15   $274.15   $274.20  
  7 purchase totals = $905.90       $994.0586   $994.06   $994.05   $994.10