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 $202.42   11.649%   $225.9999   $226.00   $226.00   $226.00  
  Purchase #2 $190.27   6.822%   $203.2502   $203.25   $203.25   $203.30  
  Purchase #3 $33.42   7.109%   $35.7958   $35.80   $35.80   $35.80  
  Purchase #4 $247.38   12.816%   $279.0842   $279.08   $279.10   $279.10  
  Purchase #5 $133.64   6.150%   $141.8589   $141.86   $141.85   $141.90  
  Purchase #6 $18.30   5.180%   $19.2479   $19.25   $19.25   $19.20  
  Purchase #7 $179.65   8.564%   $195.0352   $195.04   $195.05   $195.00  
  7 purchase totals = $1,005.08       $1,100.2721   $1,100.28   $1,100.30   $1,100.30