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 $46.66   5.483%   $49.2184   $49.22   $49.20   $49.20  
  Purchase #2 $245.95   4.275%   $256.4644   $256.46   $256.45   $256.50  
  Purchase #3 $75.82   5.572%   $80.0447   $80.04   $80.05   $80.00  
  Purchase #4 $239.49   11.869%   $267.9151   $267.92   $267.90   $267.90  
  Purchase #5 $94.59   12.170%   $106.1016   $106.10   $106.10   $106.10  
  Purchase #6 $159.27   6.617%   $169.8089   $169.81   $169.80   $169.80  
  Purchase #7 $101.27   8.351%   $109.7271   $109.73   $109.75   $109.70  
  7 purchase totals = $963.05       $1,039.2802   $1,039.28   $1,039.25   $1,039.20