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 $90.67   3.655%   $93.984   $93.98   $94.00   $94.00  
  Purchase #2 $194.78   13.574%   $221.2194   $221.22   $221.20   $221.20  
  Purchase #3 $160.47   4.546%   $167.765   $167.77   $167.75   $167.80  
  Purchase #4 $192.41   3.173%   $198.5152   $198.52   $198.50   $198.50  
  Purchase #5 $72.91   12.744%   $82.2017   $82.20   $82.20   $82.20  
  Purchase #6 $231.96   3.120%   $239.1972   $239.20   $239.20   $239.20  
  Purchase #7 $239.82   6.737%   $255.9767   $255.98   $256.00   $256.00  
  7 purchase totals = $1,183.02       $1,258.8592   $1,258.87   $1,258.85   $1,258.90