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 $247.84   8.165%   $268.0761   $268.08   $268.10   $268.10  
  Purchase #2 $232.37   13.754%   $264.3302   $264.33   $264.35   $264.30  
  Purchase #3 $191.37   3.645%   $198.3454   $198.35   $198.35   $198.30  
  Purchase #4 $43.88   4.371%   $45.798   $45.80   $45.80   $45.80  
  Purchase #5 $216.77   6.842%   $231.6014   $231.60   $231.60   $231.60  
  Purchase #6 $123.64   10.411%   $136.5122   $136.51   $136.50   $136.50  
  Purchase #7 $115.33   3.611%   $119.4946   $119.49   $119.50   $119.50  
  7 purchase totals = $1,171.20       $1,264.1579   $1,264.16   $1,264.20   $1,264.10