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 $139.83   5.135%   $147.0103   $147.01   $147.00   $147.00  
  Purchase #2 $160.52   3.290%   $165.8011   $165.80   $165.80   $165.80  
  Purchase #3 $23.36   5.745%   $24.702   $24.70   $24.70   $24.70  
  Purchase #4 $118.44   6.152%   $125.7264   $125.73   $125.75   $125.70  
  Purchase #5 $247.37   13.536%   $280.854   $280.85   $280.85   $280.90  
  Purchase #6 $135.33   4.822%   $141.8556   $141.86   $141.85   $141.90  
  Purchase #7 $97.37   11.486%   $108.5539   $108.55   $108.55   $108.60  
  7 purchase totals = $922.22       $994.5033   $994.50   $994.50   $994.60