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 $117.56   6.681%   $125.4142   $125.41   $125.40   $125.40  
  Purchase #2 $190.60   8.305%   $206.4293   $206.43   $206.45   $206.40  
  Purchase #3 $63.54   3.323%   $65.6514   $65.65   $65.65   $65.70  
  Purchase #4 $202.47   8.501%   $219.682   $219.68   $219.70   $219.70  
  Purchase #5 $52.61   10.524%   $58.1467   $58.15   $58.15   $58.10  
  Purchase #6 $161.98   8.851%   $176.3168   $176.32   $176.30   $176.30  
  Purchase #7 $221.78   8.485%   $240.598   $240.60   $240.60   $240.60  
  7 purchase totals = $1,010.54       $1,092.2384   $1,092.24   $1,092.25   $1,092.20