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 $145.41   6.361%   $154.6595   $154.66   $154.65   $154.70  
  Purchase #2 $230.55   13.396%   $261.4345   $261.43   $261.45   $261.40  
  Purchase #3 $32.75   6.465%   $34.8673   $34.87   $34.85   $34.90  
  Purchase #4 $119.40   7.511%   $128.3681   $128.37   $128.35   $128.40  
  Purchase #5 $185.48   12.686%   $209.01   $209.01   $209.00   $209.00  
  Purchase #6 $199.52   3.738%   $206.9781   $206.98   $207.00   $207.00  
  Purchase #7 $49.92   3.815%   $51.8244   $51.82   $51.80   $51.80  
  7 purchase totals = $963.03       $1,047.1419   $1,047.14   $1,047.10   $1,047.20