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 $208.52   8.645%   $226.5466   $226.55   $226.55   $226.50  
  Purchase #2 $57.41   7.759%   $61.8644   $61.86   $61.85   $61.90  
  Purchase #3 $206.94   4.129%   $215.4846   $215.48   $215.50   $215.50  
  Purchase #4 $5.54   6.114%   $5.8787   $5.88   $5.90   $5.90  
  Purchase #5 $34.77   12.705%   $39.1875   $39.19   $39.20   $39.20  
  Purchase #6 $207.97   6.673%   $221.8478   $221.85   $221.85   $221.80  
  Purchase #7 $26.87   13.840%   $30.5888   $30.59   $30.60   $30.60  
  7 purchase totals = $748.02       $801.3984   $801.40   $801.45   $801.40