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 $180.57   8.293%   $195.5447   $195.54   $195.55   $195.50  
  Purchase #2 $25.88   3.314%   $26.7377   $26.74   $26.75   $26.70  
  Purchase #3 $156.52   13.163%   $177.1227   $177.12   $177.10   $177.10  
  Purchase #4 $239.76   4.285%   $250.0337   $250.03   $250.05   $250.00  
  Purchase #5 $240.99   11.341%   $268.3207   $268.32   $268.30   $268.30  
  Purchase #6 $99.66   5.352%   $104.9938   $104.99   $105.00   $105.00  
  Purchase #7 $11.92   5.244%   $12.5451   $12.55   $12.55   $12.50  
  7 purchase totals = $955.30       $1,035.2984   $1,035.29   $1,035.30   $1,035.10