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 $186.73   10.294%   $205.952   $205.95   $205.95   $206.00  
  Purchase #2 $49.40   13.109%   $55.8758   $55.88   $55.90   $55.90  
  Purchase #3 $102.39   4.780%   $107.2842   $107.28   $107.30   $107.30  
  Purchase #4 $206.38   8.561%   $224.0482   $224.05   $224.05   $224.00  
  Purchase #5 $214.88   5.426%   $226.5394   $226.54   $226.55   $226.50  
  Purchase #6 $203.30   6.122%   $215.746   $215.75   $215.75   $215.70  
  Purchase #7 $219.90   3.846%   $228.3574   $228.36   $228.35   $228.40  
  7 purchase totals = $1,182.98       $1,263.8030   $1,263.81   $1,263.85   $1,263.80