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 $169.98   8.283%   $184.0594   $184.06   $184.05   $184.10  
  Purchase #2 $85.66   8.144%   $92.6362   $92.64   $92.65   $92.60  
  Purchase #3 $81.32   13.166%   $92.0266   $92.03   $92.05   $92.00  
  Purchase #4 $119.83   3.739%   $124.3104   $124.31   $124.30   $124.30  
  Purchase #5 $179.70   8.263%   $194.5486   $194.55   $194.55   $194.50  
  Purchase #6 $217.94   12.361%   $244.8796   $244.88   $244.90   $244.90  
  Purchase #7 $159.52   4.438%   $166.5995   $166.60   $166.60   $166.60  
  7 purchase totals = $1,013.95       $1,099.0603   $1,099.07   $1,099.10   $1,099.00