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 $134.99   9.133%   $147.3186   $147.32   $147.30   $147.30  
  Purchase #2 $119.84   3.825%   $124.4239   $124.42   $124.40   $124.40  
  Purchase #3 $68.61   10.326%   $75.6947   $75.69   $75.70   $75.70  
  Purchase #4 $227.91   3.450%   $235.7729   $235.77   $235.75   $235.80  
  Purchase #5 $117.75   11.794%   $131.6374   $131.64   $131.65   $131.60  
  Purchase #6 $186.48   12.135%   $209.1093   $209.11   $209.10   $209.10  
  Purchase #7 $28.31   9.254%   $30.9298   $30.93   $30.95   $30.90  
  7 purchase totals = $883.89       $954.8866   $954.88   $954.85   $954.80