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 $203.27   6.269%   $216.013   $216.01   $216.00   $216.00  
  Purchase #2 $61.71   6.170%   $65.5175   $65.52   $65.50   $65.50  
  Purchase #3 $90.97   5.241%   $95.7377   $95.74   $95.75   $95.70  
  Purchase #4 $223.48   13.658%   $254.0029   $254.00   $254.00   $254.00  
  Purchase #5 $99.30   12.231%   $111.4454   $111.45   $111.45   $111.40  
  Purchase #6 $133.65   8.249%   $144.6748   $144.67   $144.65   $144.70  
  Purchase #7 $97.81   9.794%   $107.3895   $107.39   $107.40   $107.40  
  7 purchase totals = $910.19       $994.7808   $994.78   $994.75   $994.70