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 $206.82   13.306%   $234.3395   $234.34   $234.35   $234.30  
  Purchase #2 $164.49   5.799%   $174.0288   $174.03   $174.05   $174.00  
  Purchase #3 $13.25   6.793%   $14.1501   $14.15   $14.15   $14.20  
  Purchase #4 $219.64   7.121%   $235.2806   $235.28   $235.30   $235.30  
  Purchase #5 $184.50   9.685%   $202.3688   $202.37   $202.35   $202.40  
  Purchase #6 $101.94   3.510%   $105.5181   $105.52   $105.50   $105.50  
  Purchase #7 $9.73   11.154%   $10.8153   $10.82   $10.80   $10.80  
  7 purchase totals = $900.37       $976.5012   $976.51   $976.50   $976.50