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 $85.51   10.445%   $94.4415   $94.44   $94.45   $94.40  
  Purchase #2 $203.92   13.633%   $231.7204   $231.72   $231.70   $231.70  
  Purchase #3 $156.66   3.166%   $161.6199   $161.62   $161.60   $161.60  
  Purchase #4 $24.89   9.642%   $27.2899   $27.29   $27.30   $27.30  
  Purchase #5 $164.76   12.753%   $185.7718   $185.77   $185.75   $185.80  
  Purchase #6 $156.67   13.263%   $177.4491   $177.45   $177.45   $177.40  
  Purchase #7 $154.82   6.431%   $164.7765   $164.78   $164.80   $164.80  
  7 purchase totals = $947.23       $1,043.0691   $1,043.07   $1,043.05   $1,043.00