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 $213.54   8.705%   $232.1287   $232.13   $232.15   $232.10  
  Purchase #2 $175.72   11.338%   $195.6431   $195.64   $195.65   $195.60  
  Purchase #3 $13.27   9.556%   $14.5381   $14.54   $14.55   $14.50  
  Purchase #4 $52.99   9.655%   $58.1062   $58.11   $58.10   $58.10  
  Purchase #5 $74.75   7.238%   $80.1604   $80.16   $80.15   $80.20  
  Purchase #6 $68.97   9.706%   $75.6642   $75.66   $75.65   $75.70  
  Purchase #7 $72.28   7.754%   $77.8846   $77.88   $77.90   $77.90  
  7 purchase totals = $671.52       $734.1253   $734.12   $734.15   $734.10