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 $202.46   6.823%   $216.2738   $216.27   $216.25   $216.30  
  Purchase #2 $159.27   3.302%   $164.5291   $164.53   $164.55   $164.50  
  Purchase #3 $148.68   4.256%   $155.0078   $155.01   $155.00   $155.00  
  Purchase #4 $230.51   8.575%   $250.2762   $250.28   $250.30   $250.30  
  Purchase #5 $169.85   3.305%   $175.4635   $175.46   $175.45   $175.50  
  Purchase #6 $12.85   3.331%   $13.278   $13.28   $13.30   $13.30  
  Purchase #7 $204.67   10.620%   $226.406   $226.41   $226.40   $226.40  
  7 purchase totals = $1,128.29       $1,201.2344   $1,201.24   $1,201.25   $1,201.30