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 $229.59   6.413%   $244.3136   $244.31   $244.30   $244.30  
  Purchase #2 $113.79   9.293%   $124.3645   $124.36   $124.35   $124.40  
  Purchase #3 $169.25   6.637%   $180.4831   $180.48   $180.50   $180.50  
  Purchase #4 $157.80   11.613%   $176.1253   $176.13   $176.15   $176.10  
  Purchase #5 $102.86   5.556%   $108.5749   $108.57   $108.55   $108.60  
  Purchase #6 $25.39   3.219%   $26.2073   $26.21   $26.20   $26.20  
  Purchase #7 $146.29   11.292%   $162.8091   $162.81   $162.80   $162.80  
  7 purchase totals = $944.97       $1,022.8778   $1,022.87   $1,022.85   $1,022.90