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 $229.84   10.146%   $253.1596   $253.16   $253.15   $253.20  
  Purchase #2 $159.48   9.237%   $174.2112   $174.21   $174.20   $174.20  
  Purchase #3 $115.89   11.865%   $129.6403   $129.64   $129.65   $129.60  
  Purchase #4 $168.97   3.111%   $174.2267   $174.23   $174.25   $174.20  
  Purchase #5 $123.35   13.209%   $139.6433   $139.64   $139.65   $139.60  
  Purchase #6 $145.30   12.498%   $163.4596   $163.46   $163.45   $163.50  
  Purchase #7 $42.73   6.218%   $45.387   $45.39   $45.40   $45.40  
  7 purchase totals = $985.56       $1,079.7277   $1,079.73   $1,079.75   $1,079.70