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 $105.84   12.615%   $119.1917   $119.19   $119.20   $119.20  
  Purchase #2 $31.48   13.173%   $35.6269   $35.63   $35.65   $35.60  
  Purchase #3 $213.53   11.516%   $238.1201   $238.12   $238.10   $238.10  
  Purchase #4 $43.54   8.615%   $47.291   $47.29   $47.30   $47.30  
  Purchase #5 $54.78   4.784%   $57.4007   $57.40   $57.40   $57.40  
  Purchase #6 $142.47   4.617%   $149.0478   $149.05   $149.05   $149.00  
  Purchase #7 $163.78   12.248%   $183.8398   $183.84   $183.85   $183.80  
  7 purchase totals = $755.42       $830.5180   $830.52   $830.55   $830.40