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 $84.78   10.293%   $93.5064   $93.51   $93.50   $93.50  
  Purchase #2 $43.56   5.155%   $45.8055   $45.81   $45.80   $45.80  
  Purchase #3 $11.79   8.596%   $12.8035   $12.80   $12.80   $12.80  
  Purchase #4 $89.95   8.643%   $97.7244   $97.72   $97.70   $97.70  
  Purchase #5 $61.92   13.416%   $70.2272   $70.23   $70.25   $70.20  
  Purchase #6 $53.86   6.138%   $57.1659   $57.17   $57.15   $57.20  
  Purchase #7 $96.48   7.771%   $103.9775   $103.98   $104.00   $104.00  
  7 purchase totals = $442.34       $481.2104   $481.22   $481.20   $481.20