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 $92.49   6.788%   $98.7682   $98.77   $98.75   $98.80  
  Purchase #2 $186.39   5.846%   $197.2864   $197.29   $197.30   $197.30  
  Purchase #3 $34.63   11.736%   $38.6942   $38.69   $38.70   $38.70  
  Purchase #4 $229.82   10.201%   $253.2639   $253.26   $253.25   $253.30  
  Purchase #5 $74.60   11.401%   $83.1051   $83.11   $83.10   $83.10  
  Purchase #6 $138.64   13.870%   $157.8694   $157.87   $157.85   $157.90  
  Purchase #7 $42.81   7.352%   $45.9574   $45.96   $45.95   $46.00  
  7 purchase totals = $799.38       $874.9446   $874.95   $874.90   $875.10