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 $248.85   13.841%   $283.2933   $283.29   $283.30   $283.30  
  Purchase #2 $59.57   9.130%   $65.0087   $65.01   $65.00   $65.00  
  Purchase #3 $244.84   7.194%   $262.4538   $262.45   $262.45   $262.50  
  Purchase #4 $127.40   9.767%   $139.8432   $139.84   $139.85   $139.80  
  Purchase #5 $115.30   3.354%   $119.1672   $119.17   $119.15   $119.20  
  Purchase #6 $136.44   9.174%   $148.957   $148.96   $148.95   $149.00  
  Purchase #7 $161.45   5.805%   $170.8222   $170.82   $170.80   $170.80  
  7 purchase totals = $1,093.85       $1,189.5454   $1,189.54   $1,189.50   $1,189.60