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 $178.92   12.873%   $201.9524   $201.95   $201.95   $202.00  
  Purchase #2 $55.46   4.326%   $57.8592   $57.86   $57.85   $57.90  
  Purchase #3 $150.63   4.258%   $157.0438   $157.04   $157.05   $157.00  
  Purchase #4 $26.46   11.325%   $29.4566   $29.46   $29.45   $29.50  
  Purchase #5 $84.34   4.563%   $88.1884   $88.19   $88.20   $88.20  
  Purchase #6 $240.33   13.181%   $272.0079   $272.01   $272.00   $272.00  
  Purchase #7 $224.77   8.639%   $244.1879   $244.19   $244.20   $244.20  
  7 purchase totals = $960.91       $1,050.6962   $1,050.70   $1,050.70   $1,050.80