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 $211.77   12.790%   $238.8554   $238.86   $238.85   $238.90  
  Purchase #2 $219.41   5.454%   $231.3766   $231.38   $231.40   $231.40  
  Purchase #3 $138.62   10.822%   $153.6215   $153.62   $153.60   $153.60  
  Purchase #4 $175.78   10.312%   $193.9064   $193.91   $193.90   $193.90  
  Purchase #5 $62.44   5.584%   $65.9266   $65.93   $65.95   $65.90  
  Purchase #6 $134.43   8.368%   $145.6791   $145.68   $145.70   $145.70  
  Purchase #7 $64.77   11.608%   $72.2885   $72.29   $72.30   $72.30  
  7 purchase totals = $1,007.22       $1,101.6541   $1,101.67   $1,101.70   $1,101.70