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 $44.50   8.635%   $48.3426   $48.34   $48.35   $48.30  
  Purchase #2 $154.67   10.511%   $170.9274   $170.93   $170.95   $170.90  
  Purchase #3 $142.28   10.281%   $156.9078   $156.91   $156.90   $156.90  
  Purchase #4 $109.69   5.844%   $116.1003   $116.10   $116.10   $116.10  
  Purchase #5 $87.88   9.774%   $96.4694   $96.47   $96.45   $96.50  
  Purchase #6 $199.42   12.392%   $224.1321   $224.13   $224.15   $224.10  
  Purchase #7 $239.67   13.264%   $271.4598   $271.46   $271.45   $271.50  
  7 purchase totals = $978.11       $1,084.3394   $1,084.34   $1,084.35   $1,084.30