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 $204.48   13.220%   $231.5123   $231.51   $231.50   $231.50  
  Purchase #2 $147.89   4.756%   $154.9236   $154.92   $154.90   $154.90  
  Purchase #3 $51.59   13.786%   $58.7022   $58.70   $58.70   $58.70  
  Purchase #4 $154.45   12.853%   $174.3015   $174.30   $174.30   $174.30  
  Purchase #5 $129.81   7.511%   $139.56   $139.56   $139.55   $139.60  
  Purchase #6 $184.45   11.379%   $205.4386   $205.44   $205.45   $205.40  
  Purchase #7 $176.91   6.662%   $188.6957   $188.70   $188.70   $188.70  
  7 purchase totals = $1,049.58       $1,153.1339   $1,153.13   $1,153.10   $1,153.10