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 $57.29   5.137%   $60.233   $60.23   $60.25   $60.20  
  Purchase #2 $52.69   10.755%   $58.3568   $58.36   $58.35   $58.40  
  Purchase #3 $116.81   6.131%   $123.9716   $123.97   $123.95   $124.00  
  Purchase #4 $107.46   7.182%   $115.1778   $115.18   $115.20   $115.20  
  Purchase #5 $82.73   5.449%   $87.238   $87.24   $87.25   $87.20  
  Purchase #6 $44.60   4.814%   $46.747   $46.75   $46.75   $46.70  
  Purchase #7 $106.40   13.415%   $120.6736   $120.67   $120.65   $120.70  
  7 purchase totals = $567.98       $612.3978   $612.40   $612.40   $612.40