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 $98.26   8.574%   $106.6848   $106.68   $106.70   $106.70  
  Purchase #2 $183.48   11.366%   $204.3343   $204.33   $204.35   $204.30  
  Purchase #3 $240.53   6.862%   $257.0352   $257.04   $257.05   $257.00  
  Purchase #4 $135.45   11.289%   $150.741   $150.74   $150.75   $150.70  
  Purchase #5 $214.52   5.788%   $226.9364   $226.94   $226.95   $226.90  
  Purchase #6 $114.78   5.473%   $121.0619   $121.06   $121.05   $121.10  
  Purchase #7 $205.63   9.140%   $224.4246   $224.42   $224.40   $224.40  
  7 purchase totals = $1,192.65       $1,291.2182   $1,291.21   $1,291.25   $1,291.10