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 $43.91   7.859%   $47.3609   $47.36   $47.35   $47.40  
  Purchase #2 $57.87   8.582%   $62.8364   $62.84   $62.85   $62.80  
  Purchase #3 $200.61   5.353%   $211.3487   $211.35   $211.35   $211.30  
  Purchase #4 $165.90   4.212%   $172.8877   $172.89   $172.90   $172.90  
  Purchase #5 $166.64   11.651%   $186.0552   $186.06   $186.05   $186.10  
  Purchase #6 $178.72   7.581%   $192.2688   $192.27   $192.25   $192.30  
  Purchase #7 $76.30   8.753%   $82.9785   $82.98   $83.00   $83.00  
  7 purchase totals = $889.95       $955.7362   $955.75   $955.75   $955.80