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 $84.97   11.376%   $94.6362   $94.64   $94.65   $94.60  
  Purchase #2 $231.85   11.127%   $257.6479   $257.65   $257.65   $257.60  
  Purchase #3 $210.99   4.233%   $219.9212   $219.92   $219.90   $219.90  
  Purchase #4 $215.25   12.132%   $241.3641   $241.36   $241.35   $241.40  
  Purchase #5 $106.76   6.611%   $113.8179   $113.82   $113.80   $113.80  
  Purchase #6 $113.35   7.330%   $121.6586   $121.66   $121.65   $121.70  
  Purchase #7 $32.52   11.452%   $36.2442   $36.24   $36.25   $36.20  
  7 purchase totals = $995.69       $1,085.2901   $1,085.29   $1,085.25   $1,085.20