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 $44.28   6.218%   $47.0333   $47.03   $47.05   $47.00  
  Purchase #2 $139.81   12.517%   $157.31   $157.31   $157.30   $157.30  
  Purchase #3 $45.83   8.691%   $49.8131   $49.81   $49.80   $49.80  
  Purchase #4 $167.25   5.453%   $176.3701   $176.37   $176.35   $176.40  
  Purchase #5 $189.42   10.523%   $209.3527   $209.35   $209.35   $209.40  
  Purchase #6 $53.40   9.406%   $58.4228   $58.42   $58.40   $58.40  
  Purchase #7 $153.31   11.117%   $170.3535   $170.35   $170.35   $170.40  
  7 purchase totals = $793.30       $868.6555   $868.64   $868.60   $868.70