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 $41.39   6.673%   $44.152   $44.15   $44.15   $44.20  
  Purchase #2 $14.76   10.140%   $16.2567   $16.26   $16.25   $16.30  
  Purchase #3 $166.41   4.601%   $174.0665   $174.07   $174.05   $174.10  
  Purchase #4 $59.96   8.181%   $64.8653   $64.87   $64.85   $64.90  
  Purchase #5 $77.92   9.400%   $85.2445   $85.24   $85.25   $85.20  
  Purchase #6 $56.90   11.252%   $63.3024   $63.30   $63.30   $63.30  
  Purchase #7 $5.65   10.860%   $6.2636   $6.26   $6.25   $6.30  
  7 purchase totals = $422.99       $454.1510   $454.15   $454.10   $454.30