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 $240.59   10.385%   $265.5753   $265.58   $265.60   $265.60  
  Purchase #2 $225.77   9.292%   $246.7485   $246.75   $246.75   $246.70  
  Purchase #3 $44.84   4.497%   $46.8565   $46.86   $46.85   $46.90  
  Purchase #4 $246.85   11.390%   $274.9662   $274.97   $274.95   $275.00  
  Purchase #5 $105.56   9.781%   $115.8848   $115.88   $115.90   $115.90  
  Purchase #6 $7.61   3.679%   $7.89   $7.89   $7.90   $7.90  
  Purchase #7 $93.89   3.141%   $96.8391   $96.84   $96.85   $96.80  
  7 purchase totals = $965.11       $1,054.7604   $1,054.77   $1,054.80   $1,054.80