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 $65.44   3.277%   $67.5845   $67.58   $67.60   $67.60  
  Purchase #2 $239.51   5.847%   $253.5141   $253.51   $253.50   $253.50  
  Purchase #3 $51.80   4.684%   $54.2263   $54.23   $54.25   $54.20  
  Purchase #4 $58.90   4.801%   $61.7278   $61.73   $61.75   $61.70  
  Purchase #5 $187.79   7.399%   $201.6846   $201.68   $201.70   $201.70  
  Purchase #6 $177.61   13.206%   $201.0652   $201.07   $201.05   $201.10  
  Purchase #7 $179.39   9.266%   $196.0123   $196.01   $196.00   $196.00  
  7 purchase totals = $960.44       $1,035.8148   $1,035.81   $1,035.85   $1,035.80