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 $181.88   6.652%   $193.9787   $193.98   $194.00   $194.00  
  Purchase #2 $224.75   7.202%   $240.9365   $240.94   $240.95   $240.90  
  Purchase #3 $204.76   11.752%   $228.8234   $228.82   $228.80   $228.80  
  Purchase #4 $59.73   5.731%   $63.1531   $63.15   $63.15   $63.20  
  Purchase #5 $223.41   8.734%   $242.9226   $242.92   $242.90   $242.90  
  Purchase #6 $104.38   5.120%   $109.7243   $109.72   $109.70   $109.70  
  Purchase #7 $169.42   7.299%   $181.786   $181.79   $181.80   $181.80  
  7 purchase totals = $1,168.33       $1,261.3246   $1,261.32   $1,261.30   $1,261.30