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 $83.42   13.411%   $94.6075   $94.61   $94.60   $94.60  
  Purchase #2 $232.55   3.489%   $240.6637   $240.66   $240.65   $240.70  
  Purchase #3 $207.60   9.113%   $226.5186   $226.52   $226.50   $226.50  
  Purchase #4 $101.33   8.508%   $109.9512   $109.95   $109.95   $110.00  
  Purchase #5 $53.26   5.351%   $56.1099   $56.11   $56.10   $56.10  
  Purchase #6 $128.61   10.756%   $142.4433   $142.44   $142.45   $142.40  
  Purchase #7 $67.73   6.159%   $71.9015   $71.90   $71.90   $71.90  
  7 purchase totals = $874.50       $942.1957   $942.19   $942.15   $942.20