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 $232.79   8.328%   $252.1768   $252.18   $252.20   $252.20  
  Purchase #2 $119.93   12.598%   $135.0388   $135.04   $135.05   $135.00  
  Purchase #3 $33.53   8.356%   $36.3318   $36.33   $36.35   $36.30  
  Purchase #4 $194.57   3.424%   $201.2321   $201.23   $201.25   $201.20  
  Purchase #5 $223.45   13.584%   $253.8034   $253.80   $253.80   $253.80  
  Purchase #6 $13.32   8.506%   $14.453   $14.45   $14.45   $14.50  
  Purchase #7 $207.27   4.337%   $216.2593   $216.26   $216.25   $216.30  
  7 purchase totals = $1,024.86       $1,109.2952   $1,109.29   $1,109.35   $1,109.30