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 $152.30   11.339%   $169.5693   $169.57   $169.55   $169.60  
  Purchase #2 $93.65   9.679%   $102.7144   $102.71   $102.70   $102.70  
  Purchase #3 $65.50   4.453%   $68.4167   $68.42   $68.40   $68.40  
  Purchase #4 $14.97   12.186%   $16.7942   $16.79   $16.80   $16.80  
  Purchase #5 $58.49   6.858%   $62.5012   $62.50   $62.50   $62.50  
  Purchase #6 $107.26   10.764%   $118.8055   $118.81   $118.80   $118.80  
  Purchase #7 $241.39   4.494%   $252.2381   $252.24   $252.25   $252.20  
  7 purchase totals = $733.56       $791.0394   $791.04   $791.00   $791.00