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 $180.93   6.321%   $192.3666   $192.37   $192.35   $192.40  
  Purchase #2 $90.60   6.621%   $96.5986   $96.60   $96.60   $96.60  
  Purchase #3 $23.31   13.769%   $26.5196   $26.52   $26.50   $26.50  
  Purchase #4 $243.69   4.563%   $254.8096   $254.81   $254.80   $254.80  
  Purchase #5 $24.85   13.352%   $28.168   $28.17   $28.15   $28.20  
  Purchase #6 $71.37   6.378%   $75.922   $75.92   $75.90   $75.90  
  Purchase #7 $131.52   6.450%   $140.003   $140.00   $140.00   $140.00  
  7 purchase totals = $766.27       $814.3874   $814.39   $814.30   $814.40