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 $73.97   3.827%   $76.8008   $76.80   $76.80   $76.80  
  Purchase #2 $29.82   11.424%   $33.2266   $33.23   $33.25   $33.20  
  Purchase #3 $69.31   3.714%   $71.8842   $71.88   $71.90   $71.90  
  Purchase #4 $232.56   5.221%   $244.702   $244.70   $244.70   $244.70  
  Purchase #5 $181.62   4.562%   $189.9055   $189.91   $189.90   $189.90  
  Purchase #6 $171.98   13.344%   $194.929   $194.93   $194.95   $194.90  
  Purchase #7 $250.66   9.225%   $273.7834   $273.78   $273.80   $273.80  
  7 purchase totals = $1,009.92       $1,085.2315   $1,085.23   $1,085.30   $1,085.20