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 $135.73   9.763%   $148.9813   $148.98   $149.00   $149.00  
  Purchase #2 $225.81   6.373%   $240.2009   $240.20   $240.20   $240.20  
  Purchase #3 $175.49   8.828%   $190.9823   $190.98   $191.00   $191.00  
  Purchase #4 $112.70   3.759%   $116.9364   $116.94   $116.95   $116.90  
  Purchase #5 $64.88   13.843%   $73.8613   $73.86   $73.85   $73.90  
  Purchase #6 $6.58   10.309%   $7.2583   $7.26   $7.25   $7.30  
  Purchase #7 $236.91   13.779%   $269.5538   $269.55   $269.55   $269.60  
  7 purchase totals = $958.10       $1,047.7743   $1,047.77   $1,047.80   $1,047.90