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 $63.96   10.517%   $70.6867   $70.69   $70.70   $70.70  
  Purchase #2 $98.77   13.691%   $112.2926   $112.29   $112.30   $112.30  
  Purchase #3 $7.58   3.447%   $7.8413   $7.84   $7.85   $7.80  
  Purchase #4 $239.26   5.475%   $252.3595   $252.36   $252.35   $252.40  
  Purchase #5 $234.85   7.816%   $253.2059   $253.21   $253.20   $253.20  
  Purchase #6 $223.98   11.364%   $249.4331   $249.43   $249.45   $249.40  
  Purchase #7 $82.95   6.212%   $88.1029   $88.10   $88.10   $88.10  
  7 purchase totals = $951.35       $1,033.9220   $1,033.92   $1,033.95   $1,033.90