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 $199.28   13.305%   $225.7942   $225.79   $225.80   $225.80  
  Purchase #2 $163.32   8.772%   $177.6464   $177.65   $177.65   $177.60  
  Purchase #3 $44.47   8.515%   $48.2566   $48.26   $48.25   $48.30  
  Purchase #4 $38.56   6.874%   $41.2106   $41.21   $41.20   $41.20  
  Purchase #5 $110.96   12.831%   $125.1973   $125.20   $125.20   $125.20  
  Purchase #6 $181.54   13.853%   $206.6887   $206.69   $206.70   $206.70  
  Purchase #7 $223.28   7.756%   $240.5976   $240.60   $240.60   $240.60  
  7 purchase totals = $961.41       $1,065.3914   $1,065.40   $1,065.40   $1,065.40