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 $65.87   6.247%   $69.9849   $69.98   $70.00   $70.00  
  Purchase #2 $130.95   11.607%   $146.1494   $146.15   $146.15   $146.10  
  Purchase #3 $53.31   13.322%   $60.412   $60.41   $60.40   $60.40  
  Purchase #4 $142.58   13.143%   $161.3193   $161.32   $161.30   $161.30  
  Purchase #5 $86.92   5.467%   $91.6719   $91.67   $91.65   $91.70  
  Purchase #6 $124.40   5.589%   $131.3527   $131.35   $131.35   $131.40  
  Purchase #7 $47.73   11.506%   $53.2218   $53.22   $53.20   $53.20  
  7 purchase totals = $651.76       $714.1120   $714.10   $714.05   $714.10