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 $51.37   3.174%   $53.0005   $53.00   $53.00   $53.00  
  Purchase #2 $44.69   6.466%   $47.5797   $47.58   $47.60   $47.60  
  Purchase #3 $74.76   7.264%   $80.1906   $80.19   $80.20   $80.20  
  Purchase #4 $156.72   8.262%   $169.6682   $169.67   $169.65   $169.70  
  Purchase #5 $178.81   12.173%   $200.5765   $200.58   $200.60   $200.60  
  Purchase #6 $245.25   9.534%   $268.6321   $268.63   $268.65   $268.60  
  Purchase #7 $194.47   6.385%   $206.8869   $206.89   $206.90   $206.90  
  7 purchase totals = $946.07       $1,026.5345   $1,026.54   $1,026.60   $1,026.60