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 $211.52   13.253%   $239.5527   $239.55   $239.55   $239.60  
  Purchase #2 $139.35   13.858%   $158.6611   $158.66   $158.65   $158.70  
  Purchase #3 $47.39   3.453%   $49.0264   $49.03   $49.05   $49.00  
  Purchase #4 $189.87   11.140%   $211.0215   $211.02   $211.00   $211.00  
  Purchase #5 $68.72   7.480%   $73.8603   $73.86   $73.85   $73.90  
  Purchase #6 $190.77   9.797%   $209.4597   $209.46   $209.45   $209.50  
  Purchase #7 $105.48   4.514%   $110.2414   $110.24   $110.25   $110.20  
  7 purchase totals = $953.10       $1,051.8231   $1,051.82   $1,051.80   $1,051.90