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 $93.76   11.455%   $104.5002   $104.50   $104.50   $104.50  
  Purchase #2 $124.59   9.212%   $136.0672   $136.07   $136.05   $136.10  
  Purchase #3 $189.53   5.445%   $199.8499   $199.85   $199.85   $199.80  
  Purchase #4 $219.39   6.103%   $232.7794   $232.78   $232.80   $232.80  
  Purchase #5 $124.96   13.121%   $141.356   $141.36   $141.35   $141.40  
  Purchase #6 $196.82   4.641%   $205.9544   $205.95   $205.95   $206.00  
  Purchase #7 $173.26   9.250%   $189.2866   $189.29   $189.30   $189.30  
  7 purchase totals = $1,122.31       $1,209.7937   $1,209.80   $1,209.80   $1,209.90