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 $65.47   9.771%   $71.8671   $71.87   $71.85   $71.90  
  Purchase #2 $242.98   3.441%   $251.3409   $251.34   $251.35   $251.30  
  Purchase #3 $170.65   8.177%   $184.6041   $184.60   $184.60   $184.60  
  Purchase #4 $32.96   8.833%   $35.8714   $35.87   $35.85   $35.90  
  Purchase #5 $96.54   10.496%   $106.6728   $106.67   $106.65   $106.70  
  Purchase #6 $173.62   4.176%   $180.8704   $180.87   $180.85   $180.90  
  Purchase #7 $120.85   12.290%   $135.7025   $135.70   $135.70   $135.70  
  7 purchase totals = $903.07       $966.9292   $966.92   $966.85   $967.00