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 $56.95   12.849%   $64.2675   $64.27   $64.25   $64.30  
  Purchase #2 $224.60   4.202%   $234.0377   $234.04   $234.05   $234.00  
  Purchase #3 $236.36   3.321%   $244.2095   $244.21   $244.20   $244.20  
  Purchase #4 $142.79   3.399%   $147.6434   $147.64   $147.65   $147.60  
  Purchase #5 $195.86   11.137%   $217.6729   $217.67   $217.65   $217.70  
  Purchase #6 $165.61   5.410%   $174.5695   $174.57   $174.55   $174.60  
  Purchase #7 $74.78   3.157%   $77.1408   $77.14   $77.15   $77.10  
  7 purchase totals = $1,096.95       $1,159.5413   $1,159.54   $1,159.50   $1,159.50