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 $86.92   10.240%   $95.8206   $95.82   $95.80   $95.80  
  Purchase #2 $220.92   3.796%   $229.3061   $229.31   $229.30   $229.30  
  Purchase #3 $42.87   3.432%   $44.3413   $44.34   $44.35   $44.30  
  Purchase #4 $164.61   10.269%   $181.5138   $181.51   $181.50   $181.50  
  Purchase #5 $61.38   12.613%   $69.1219   $69.12   $69.10   $69.10  
  Purchase #6 $223.32   12.179%   $250.5181   $250.52   $250.50   $250.50  
  Purchase #7 $117.27   7.511%   $126.0781   $126.08   $126.10   $126.10  
  7 purchase totals = $917.29       $996.6999   $996.70   $996.65   $996.60