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 $52.77   13.733%   $60.0169   $60.02   $60.00   $60.00  
  Purchase #2 $220.31   9.682%   $241.6404   $241.64   $241.65   $241.60  
  Purchase #3 $131.41   7.349%   $141.0673   $141.07   $141.05   $141.10  
  Purchase #4 $154.71   13.128%   $175.0203   $175.02   $175.00   $175.00  
  Purchase #5 $205.91   13.815%   $234.3565   $234.36   $234.35   $234.40  
  Purchase #6 $118.83   5.874%   $125.8101   $125.81   $125.80   $125.80  
  Purchase #7 $147.55   8.475%   $160.0549   $160.05   $160.05   $160.10  
  7 purchase totals = $1,031.49       $1,137.9664   $1,137.97   $1,137.90   $1,138.00