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 $62.98   10.233%   $69.4247   $69.42   $69.40   $69.40  
  Purchase #2 $75.55   4.448%   $78.9105   $78.91   $78.90   $78.90  
  Purchase #3 $85.59   7.251%   $91.7961   $91.80   $91.80   $91.80  
  Purchase #4 $114.41   4.849%   $119.9577   $119.96   $119.95   $120.00  
  Purchase #5 $219.65   11.390%   $244.6681   $244.67   $244.65   $244.70  
  Purchase #6 $45.80   5.142%   $48.155   $48.16   $48.15   $48.20  
  Purchase #7 $175.35   12.255%   $196.8391   $196.84   $196.85   $196.80  
  7 purchase totals = $779.33       $849.7512   $849.76   $849.70   $849.80