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 $87.44   10.540%   $96.6562   $96.66   $96.65   $96.70  
  Purchase #2 $231.30   8.210%   $250.2897   $250.29   $250.30   $250.30  
  Purchase #3 $250.92   3.589%   $259.9255   $259.93   $259.95   $259.90  
  Purchase #4 $118.43   3.388%   $122.4424   $122.44   $122.45   $122.40  
  Purchase #5 $74.88   10.388%   $82.6585   $82.66   $82.65   $82.70  
  Purchase #6 $96.75   5.334%   $101.9106   $101.91   $101.90   $101.90  
  Purchase #7 $226.82   10.858%   $251.4481   $251.45   $251.45   $251.40  
  7 purchase totals = $1,086.54       $1,165.3310   $1,165.34   $1,165.35   $1,165.30