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 $227.59   8.482%   $246.8942   $246.89   $246.90   $246.90  
  Purchase #2 $157.48   9.814%   $172.9351   $172.94   $172.95   $172.90  
  Purchase #3 $204.34   4.708%   $213.9603   $213.96   $213.95   $214.00  
  Purchase #4 $104.42   12.668%   $117.6479   $117.65   $117.65   $117.60  
  Purchase #5 $241.76   6.547%   $257.588   $257.59   $257.60   $257.60  
  Purchase #6 $87.37   9.246%   $95.4482   $95.45   $95.45   $95.40  
  Purchase #7 $86.91   3.331%   $89.805   $89.81   $89.80   $89.80  
  7 purchase totals = $1,109.87       $1,194.2787   $1,194.29   $1,194.30   $1,194.20