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 $8.61   10.694%   $9.5308   $9.53   $9.55   $9.50  
  Purchase #2 $187.51   4.335%   $195.6386   $195.64   $195.65   $195.60  
  Purchase #3 $184.52   5.775%   $195.176   $195.18   $195.20   $195.20  
  Purchase #4 $68.71   8.197%   $74.3422   $74.34   $74.35   $74.30  
  Purchase #5 $87.55   9.874%   $96.1947   $96.19   $96.20   $96.20  
  Purchase #6 $192.65   11.577%   $214.9531   $214.95   $214.95   $215.00  
  Purchase #7 $228.74   8.676%   $248.5855   $248.59   $248.60   $248.60  
  7 purchase totals = $958.29       $1,034.4209   $1,034.42   $1,034.50   $1,034.40