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 $84.53   12.759%   $95.3152   $95.32   $95.30   $95.30  
  Purchase #2 $226.77   12.409%   $254.9099   $254.91   $254.90   $254.90  
  Purchase #3 $39.54   7.865%   $42.6498   $42.65   $42.65   $42.60  
  Purchase #4 $181.70   12.342%   $204.1254   $204.13   $204.15   $204.10  
  Purchase #5 $112.55   13.822%   $128.1067   $128.11   $128.10   $128.10  
  Purchase #6 $248.53   11.487%   $277.0786   $277.08   $277.10   $277.10  
  Purchase #7 $231.47   3.746%   $240.1409   $240.14   $240.15   $240.10  
  7 purchase totals = $1,125.09       $1,242.3265   $1,242.34   $1,242.35   $1,242.20