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 $210.86   6.731%   $225.053   $225.05   $225.05   $225.10  
  Purchase #2 $216.37   5.614%   $228.517   $228.52   $228.50   $228.50  
  Purchase #3 $228.52   3.851%   $237.3203   $237.32   $237.30   $237.30  
  Purchase #4 $206.29   8.872%   $224.592   $224.59   $224.60   $224.60  
  Purchase #5 $51.41   13.472%   $58.336   $58.34   $58.35   $58.30  
  Purchase #6 $97.87   11.672%   $109.2934   $109.29   $109.30   $109.30  
  Purchase #7 $156.47   12.363%   $175.8144   $175.81   $175.80   $175.80  
  7 purchase totals = $1,167.79       $1,258.9261   $1,258.92   $1,258.90   $1,258.90