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 $80.82   13.325%   $91.5893   $91.59   $91.60   $91.60  
  Purchase #2 $183.64   12.667%   $206.9017   $206.90   $206.90   $206.90  
  Purchase #3 $48.35   9.845%   $53.1101   $53.11   $53.10   $53.10  
  Purchase #4 $86.89   9.127%   $94.8205   $94.82   $94.80   $94.80  
  Purchase #5 $169.25   4.407%   $176.7088   $176.71   $176.70   $176.70  
  Purchase #6 $218.35   6.274%   $232.0493   $232.05   $232.05   $232.00  
  Purchase #7 $90.52   5.631%   $95.6172   $95.62   $95.60   $95.60  
  7 purchase totals = $877.82       $950.7969   $950.80   $950.75   $950.70