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 $54.69   9.664%   $59.9752   $59.98   $60.00   $60.00  
  Purchase #2 $193.96   4.649%   $202.9772   $202.98   $203.00   $203.00  
  Purchase #3 $18.72   5.146%   $19.6833   $19.68   $19.70   $19.70  
  Purchase #4 $52.96   11.689%   $59.1505   $59.15   $59.15   $59.20  
  Purchase #5 $8.54   12.706%   $9.6251   $9.63   $9.65   $9.60  
  Purchase #6 $81.43   12.862%   $91.9035   $91.90   $91.90   $91.90  
  Purchase #7 $52.68   12.686%   $59.363   $59.36   $59.35   $59.40  
  7 purchase totals = $462.98       $502.6778   $502.68   $502.75   $502.80