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 $165.76   12.354%   $186.238   $186.24   $186.25   $186.20  
  Purchase #2 $98.65   6.375%   $104.9389   $104.94   $104.95   $104.90  
  Purchase #3 $180.77   5.797%   $191.2492   $191.25   $191.25   $191.20  
  Purchase #4 $213.26   4.126%   $222.0591   $222.06   $222.05   $222.10  
  Purchase #5 $240.40   8.107%   $259.8892   $259.89   $259.90   $259.90  
  Purchase #6 $178.50   9.537%   $195.5235   $195.52   $195.50   $195.50  
  Purchase #7 $186.90   8.873%   $203.4836   $203.48   $203.50   $203.50  
  7 purchase totals = $1,264.24       $1,363.3815   $1,363.38   $1,363.40   $1,363.30