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 $23.41   12.464%   $26.3278   $26.33   $26.35   $26.30  
  Purchase #2 $75.76   4.171%   $78.9199   $78.92   $78.90   $78.90  
  Purchase #3 $107.52   3.342%   $111.1133   $111.11   $111.10   $111.10  
  Purchase #4 $206.33   7.204%   $221.194   $221.19   $221.20   $221.20  
  Purchase #5 $167.60   3.479%   $173.4308   $173.43   $173.45   $173.40  
  Purchase #6 $10.85   4.184%   $11.304   $11.30   $11.30   $11.30  
  Purchase #7 $214.36   9.360%   $234.4241   $234.42   $234.40   $234.40  
  7 purchase totals = $805.83       $856.7139   $856.70   $856.70   $856.60