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 $112.45   10.524%   $124.2842   $124.28   $124.30   $124.30  
  Purchase #2 $166.76   10.262%   $183.8729   $183.87   $183.85   $183.90  
  Purchase #3 $76.76   9.393%   $83.9701   $83.97   $83.95   $84.00  
  Purchase #4 $171.95   13.381%   $194.9586   $194.96   $194.95   $195.00  
  Purchase #5 $169.93   12.387%   $190.9792   $190.98   $191.00   $191.00  
  Purchase #6 $246.98   3.178%   $254.829   $254.83   $254.85   $254.80  
  Purchase #7 $68.61   6.852%   $73.3112   $73.31   $73.30   $73.30  
  7 purchase totals = $1,013.44       $1,106.2052   $1,106.20   $1,106.20   $1,106.30