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 $89.29   8.337%   $96.7341   $96.73   $96.75   $96.70  
  Purchase #2 $92.98   5.645%   $98.2287   $98.23   $98.25   $98.20  
  Purchase #3 $7.55   13.282%   $8.5528   $8.55   $8.55   $8.60  
  Purchase #4 $232.87   7.298%   $249.8649   $249.86   $249.85   $249.90  
  Purchase #5 $72.42   3.274%   $74.791   $74.79   $74.80   $74.80  
  Purchase #6 $235.71   8.331%   $255.347   $255.35   $255.35   $255.30  
  Purchase #7 $197.47   10.791%   $218.779   $218.78   $218.80   $218.80  
  7 purchase totals = $928.29       $1,002.2975   $1,002.29   $1,002.35   $1,002.30