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 $52.55   11.806%   $58.7541   $58.75   $58.75   $58.80  
  Purchase #2 $238.28   4.297%   $248.5189   $248.52   $248.50   $248.50  
  Purchase #3 $20.87   13.814%   $23.753   $23.75   $23.75   $23.80  
  Purchase #4 $174.25   4.562%   $182.1993   $182.20   $182.20   $182.20  
  Purchase #5 $194.44   4.438%   $203.0692   $203.07   $203.05   $203.10  
  Purchase #6 $162.76   5.153%   $171.147   $171.15   $171.15   $171.10  
  Purchase #7 $11.57   5.326%   $12.1862   $12.19   $12.20   $12.20  
  7 purchase totals = $854.72       $899.6277   $899.63   $899.60   $899.70