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 $183.90   6.162%   $195.2319   $195.23   $195.25   $195.20  
  Purchase #2 $131.63   11.579%   $146.8714   $146.87   $146.85   $146.90  
  Purchase #3 $135.84   6.276%   $144.3653   $144.37   $144.35   $144.40  
  Purchase #4 $201.77   9.402%   $220.7404   $220.74   $220.75   $220.70  
  Purchase #5 $180.44   5.581%   $190.5104   $190.51   $190.50   $190.50  
  Purchase #6 $55.68   12.577%   $62.6829   $62.68   $62.70   $62.70  
  Purchase #7 $84.85   3.745%   $88.0276   $88.03   $88.05   $88.00  
  7 purchase totals = $974.11       $1,048.4299   $1,048.43   $1,048.45   $1,048.40