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 $148.66   5.575%   $156.9478   $156.95   $156.95   $156.90  
  Purchase #2 $61.94   11.614%   $69.1337   $69.13   $69.15   $69.10  
  Purchase #3 $90.76   6.212%   $96.398   $96.40   $96.40   $96.40  
  Purchase #4 $220.88   7.758%   $238.0159   $238.02   $238.00   $238.00  
  Purchase #5 $169.47   13.709%   $192.7026   $192.70   $192.70   $192.70  
  Purchase #6 $17.59   11.404%   $19.596   $19.60   $19.60   $19.60  
  Purchase #7 $175.98   10.466%   $194.3981   $194.40   $194.40   $194.40  
  7 purchase totals = $885.28       $967.1921   $967.20   $967.20   $967.10