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 $174.76   13.277%   $197.9629   $197.96   $197.95   $198.00  
  Purchase #2 $89.58   4.344%   $93.4714   $93.47   $93.45   $93.50  
  Purchase #3 $121.91   7.317%   $130.8302   $130.83   $130.85   $130.80  
  Purchase #4 $232.44   9.609%   $254.7752   $254.78   $254.80   $254.80  
  Purchase #5 $50.63   6.541%   $53.9417   $53.94   $53.95   $53.90  
  Purchase #6 $220.26   5.871%   $233.1915   $233.19   $233.20   $233.20  
  Purchase #7 $236.81   13.644%   $269.1204   $269.12   $269.10   $269.10  
  7 purchase totals = $1,126.39       $1,233.2933   $1,233.29   $1,233.30   $1,233.30