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 $68.31   6.874%   $73.0056   $73.01   $73.00   $73.00  
  Purchase #2 $106.42   12.596%   $119.8247   $119.82   $119.80   $119.80  
  Purchase #3 $129.48   10.442%   $143.0003   $143.00   $143.00   $143.00  
  Purchase #4 $138.76   10.874%   $153.8488   $153.85   $153.85   $153.80  
  Purchase #5 $63.64   13.259%   $72.078   $72.08   $72.10   $72.10  
  Purchase #6 $248.30   10.699%   $274.8656   $274.87   $274.85   $274.90  
  Purchase #7 $200.70   12.528%   $225.8437   $225.84   $225.85   $225.80  
  7 purchase totals = $955.61       $1,062.4667   $1,062.47   $1,062.45   $1,062.40