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 $200.62   8.555%   $217.783   $217.78   $217.80   $217.80  
  Purchase #2 $199.29   9.310%   $217.8439   $217.84   $217.85   $217.80  
  Purchase #3 $20.40   3.317%   $21.0767   $21.08   $21.10   $21.10  
  Purchase #4 $215.25   3.335%   $222.4286   $222.43   $222.45   $222.40  
  Purchase #5 $138.41   8.370%   $149.9949   $149.99   $150.00   $150.00  
  Purchase #6 $163.42   3.852%   $169.7149   $169.71   $169.70   $169.70  
  Purchase #7 $226.31   9.763%   $248.4046   $248.40   $248.40   $248.40  
  7 purchase totals = $1,163.70       $1,247.2466   $1,247.23   $1,247.30   $1,247.20