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 $230.81   4.751%   $241.7758   $241.78   $241.80   $241.80  
  Purchase #2 $163.88   10.230%   $180.6449   $180.64   $180.65   $180.60  
  Purchase #3 $41.84   9.216%   $45.696   $45.70   $45.70   $45.70  
  Purchase #4 $106.67   3.644%   $110.5571   $110.56   $110.55   $110.60  
  Purchase #5 $60.90   3.335%   $62.931   $62.93   $62.95   $62.90  
  Purchase #6 $44.34   7.471%   $47.6526   $47.65   $47.65   $47.70  
  Purchase #7 $13.73   10.789%   $15.2113   $15.21   $15.20   $15.20  
  7 purchase totals = $662.17       $704.4687   $704.47   $704.50   $704.50