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 $91.63   7.249%   $98.2723   $98.27   $98.25   $98.30  
  Purchase #2 $192.87   4.650%   $201.8385   $201.84   $201.85   $201.80  
  Purchase #3 $78.65   3.815%   $81.6505   $81.65   $81.65   $81.70  
  Purchase #4 $118.58   11.521%   $132.2416   $132.24   $132.25   $132.20  
  Purchase #5 $81.82   9.157%   $89.3123   $89.31   $89.30   $89.30  
  Purchase #6 $41.82   12.745%   $47.15   $47.15   $47.15   $47.20  
  Purchase #7 $22.37   12.248%   $25.1099   $25.11   $25.10   $25.10  
  7 purchase totals = $627.74       $675.5751   $675.57   $675.55   $675.60