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 $212.85   10.540%   $235.2844   $235.28   $235.30   $235.30  
  Purchase #2 $161.95   12.164%   $181.6496   $181.65   $181.65   $181.60  
  Purchase #3 $233.59   12.117%   $261.8941   $261.89   $261.90   $261.90  
  Purchase #4 $62.49   6.541%   $66.5775   $66.58   $66.60   $66.60  
  Purchase #5 $241.42   4.752%   $252.8923   $252.89   $252.90   $252.90  
  Purchase #6 $26.33   5.332%   $27.7339   $27.73   $27.75   $27.70  
  Purchase #7 $141.55   6.103%   $150.1888   $150.19   $150.20   $150.20  
  7 purchase totals = $1,080.18       $1,176.2206   $1,176.21   $1,176.30   $1,176.20