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 $211.96   11.215%   $235.7313   $235.73   $235.75   $235.70  
  Purchase #2 $204.62   6.289%   $217.4886   $217.49   $217.50   $217.50  
  Purchase #3 $196.39   4.529%   $205.2845   $205.28   $205.30   $205.30  
  Purchase #4 $18.28   7.456%   $19.643   $19.64   $19.65   $19.60  
  Purchase #5 $145.69   12.654%   $164.1256   $164.13   $164.15   $164.10  
  Purchase #6 $21.74   6.192%   $23.0861   $23.09   $23.10   $23.10  
  Purchase #7 $154.33   9.181%   $168.499   $168.50   $168.50   $168.50  
  7 purchase totals = $953.01       $1,033.8581   $1,033.86   $1,033.95   $1,033.80