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 $217.58   6.726%   $232.2144   $232.21   $232.20   $232.20  
  Purchase #2 $68.48   11.844%   $76.5908   $76.59   $76.60   $76.60  
  Purchase #3 $108.56   5.671%   $114.7164   $114.72   $114.70   $114.70  
  Purchase #4 $207.52   6.635%   $221.289   $221.29   $221.30   $221.30  
  Purchase #5 $7.70   11.179%   $8.5608   $8.56   $8.55   $8.60  
  Purchase #6 $145.89   9.435%   $159.6547   $159.65   $159.65   $159.70  
  Purchase #7 $197.48   9.693%   $216.6217   $216.62   $216.60   $216.60  
  7 purchase totals = $953.21       $1,029.6478   $1,029.64   $1,029.60   $1,029.70