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 $179.94   11.817%   $201.2035   $201.20   $201.20   $201.20  
  Purchase #2 $64.59   3.503%   $66.8526   $66.85   $66.85   $66.90  
  Purchase #3 $48.90   8.833%   $53.2193   $53.22   $53.20   $53.20  
  Purchase #4 $239.37   9.626%   $262.4118   $262.41   $262.40   $262.40  
  Purchase #5 $87.42   5.215%   $91.979   $91.98   $92.00   $92.00  
  Purchase #6 $5.47   6.641%   $5.8333   $5.83   $5.85   $5.80  
  Purchase #7 $40.73   11.846%   $45.5549   $45.55   $45.55   $45.60  
  7 purchase totals = $666.42       $727.0544   $727.04   $727.05   $727.10