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 $82.68   13.716%   $94.0204   $94.02   $94.00   $94.00  
  Purchase #2 $75.44   6.789%   $80.5616   $80.56   $80.55   $80.60  
  Purchase #3 $128.82   4.800%   $135.0034   $135.00   $135.00   $135.00  
  Purchase #4 $156.54   8.349%   $169.6095   $169.61   $169.60   $169.60  
  Purchase #5 $222.87   13.862%   $253.7642   $253.76   $253.75   $253.80  
  Purchase #6 $65.57   11.435%   $73.0679   $73.07   $73.05   $73.10  
  Purchase #7 $165.59   12.254%   $185.8814   $185.88   $185.90   $185.90  
  7 purchase totals = $897.51       $991.9084   $991.90   $991.85   $992.00