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 $48.67   8.607%   $52.859   $52.86   $52.85   $52.90  
  Purchase #2 $12.87   13.217%   $14.571   $14.57   $14.55   $14.60  
  Purchase #3 $172.36   7.520%   $185.3215   $185.32   $185.30   $185.30  
  Purchase #4 $102.73   10.356%   $113.3687   $113.37   $113.35   $113.40  
  Purchase #5 $198.91   6.407%   $211.6542   $211.65   $211.65   $211.70  
  Purchase #6 $130.51   8.671%   $141.8265   $141.83   $141.85   $141.80  
  Purchase #7 $191.88   6.814%   $204.9547   $204.95   $204.95   $205.00  
  7 purchase totals = $857.93       $924.5556   $924.55   $924.50   $924.70