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 $246.93   3.244%   $254.9404   $254.94   $254.95   $254.90  
  Purchase #2 $181.97   8.124%   $196.7532   $196.75   $196.75   $196.80  
  Purchase #3 $122.98   12.155%   $137.9282   $137.93   $137.95   $137.90  
  Purchase #4 $63.31   9.742%   $69.4777   $69.48   $69.50   $69.50  
  Purchase #5 $214.29   3.335%   $221.4366   $221.44   $221.45   $221.40  
  Purchase #6 $97.56   12.497%   $109.7521   $109.75   $109.75   $109.80  
  Purchase #7 $202.44   4.690%   $211.9344   $211.93   $211.95   $211.90  
  7 purchase totals = $1,129.48       $1,202.2226   $1,202.22   $1,202.30   $1,202.20