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 $56.51   8.458%   $61.2896   $61.29   $61.30   $61.30  
  Purchase #2 $177.29   12.460%   $199.3803   $199.38   $199.40   $199.40  
  Purchase #3 $68.36   6.776%   $72.9921   $72.99   $73.00   $73.00  
  Purchase #4 $166.95   4.135%   $173.8534   $173.85   $173.85   $173.90  
  Purchase #5 $220.31   10.589%   $243.6386   $243.64   $243.65   $243.60  
  Purchase #6 $163.68   8.585%   $177.7319   $177.73   $177.75   $177.70  
  Purchase #7 $210.62   13.515%   $239.0853   $239.09   $239.10   $239.10  
  7 purchase totals = $1,063.72       $1,167.9712   $1,167.97   $1,168.05   $1,168.00