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 $95.62   3.104%   $98.588   $98.59   $98.60   $98.60  
  Purchase #2 $22.44   11.459%   $25.0114   $25.01   $25.00   $25.00  
  Purchase #3 $111.72   12.332%   $125.4973   $125.50   $125.50   $125.50  
  Purchase #4 $135.89   8.221%   $147.0615   $147.06   $147.05   $147.10  
  Purchase #5 $243.48   11.620%   $271.7724   $271.77   $271.75   $271.80  
  Purchase #6 $71.98   4.210%   $75.0104   $75.01   $75.00   $75.00  
  Purchase #7 $47.65   4.107%   $49.607   $49.61   $49.60   $49.60  
  7 purchase totals = $728.78       $792.5480   $792.55   $792.50   $792.60