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 $135.57   5.268%   $142.7118   $142.71   $142.70   $142.70  
  Purchase #2 $200.75   5.585%   $211.9619   $211.96   $211.95   $212.00  
  Purchase #3 $215.69   13.698%   $245.2352   $245.24   $245.25   $245.20  
  Purchase #4 $20.86   4.782%   $21.8575   $21.86   $21.85   $21.90  
  Purchase #5 $202.68   10.440%   $223.8398   $223.84   $223.85   $223.80  
  Purchase #6 $86.72   5.794%   $91.7446   $91.74   $91.75   $91.70  
  Purchase #7 $32.60   5.175%   $34.2871   $34.29   $34.30   $34.30  
  7 purchase totals = $894.87       $971.6379   $971.64   $971.65   $971.60