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 $94.86   12.106%   $106.3438   $106.34   $106.35   $106.30  
  Purchase #2 $176.59   9.411%   $193.2089   $193.21   $193.20   $193.20  
  Purchase #3 $175.56   9.859%   $192.8685   $192.87   $192.85   $192.90  
  Purchase #4 $141.39   4.834%   $148.2248   $148.22   $148.20   $148.20  
  Purchase #5 $214.83   4.873%   $225.2987   $225.30   $225.30   $225.30  
  Purchase #6 $169.59   5.268%   $178.524   $178.52   $178.50   $178.50  
  Purchase #7 $195.56   4.379%   $204.1236   $204.12   $204.10   $204.10  
  7 purchase totals = $1,168.38       $1,248.5923   $1,248.58   $1,248.50   $1,248.50