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 $141.42   4.406%   $147.651   $147.65   $147.65   $147.70  
  Purchase #2 $239.36   6.821%   $255.6867   $255.69   $255.70   $255.70  
  Purchase #3 $224.54   6.865%   $239.9547   $239.95   $239.95   $240.00  
  Purchase #4 $141.64   3.414%   $146.4756   $146.48   $146.50   $146.50  
  Purchase #5 $97.84   12.268%   $109.843   $109.84   $109.85   $109.80  
  Purchase #6 $180.87   7.469%   $194.3792   $194.38   $194.40   $194.40  
  Purchase #7 $109.77   13.578%   $124.6746   $124.67   $124.65   $124.70  
  7 purchase totals = $1,135.44       $1,218.6648   $1,218.66   $1,218.70   $1,218.80