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 $63.46   9.533%   $69.5096   $69.51   $69.50   $69.50  
  Purchase #2 $109.94   7.296%   $117.9612   $117.96   $117.95   $118.00  
  Purchase #3 $165.35   8.153%   $178.831   $178.83   $178.85   $178.80  
  Purchase #4 $193.47   4.296%   $201.7815   $201.78   $201.80   $201.80  
  Purchase #5 $32.49   5.603%   $34.3104   $34.31   $34.30   $34.30  
  Purchase #6 $247.51   5.515%   $261.1602   $261.16   $261.15   $261.20  
  Purchase #7 $211.42   11.176%   $235.0483   $235.05   $235.05   $235.00  
  7 purchase totals = $1,023.64       $1,098.6022   $1,098.60   $1,098.60   $1,098.60