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 $120.60   11.138%   $134.0324   $134.03   $134.05   $134.00  
  Purchase #2 $200.69   8.463%   $217.6744   $217.67   $217.65   $217.70  
  Purchase #3 $144.96   7.798%   $156.264   $156.26   $156.25   $156.30  
  Purchase #4 $111.56   8.391%   $120.921   $120.92   $120.90   $120.90  
  Purchase #5 $154.85   9.636%   $169.7713   $169.77   $169.75   $169.80  
  Purchase #6 $24.70   9.207%   $26.9741   $26.97   $26.95   $27.00  
  Purchase #7 $149.28   13.762%   $169.8239   $169.82   $169.80   $169.80  
  7 purchase totals = $906.64       $995.4611   $995.44   $995.35   $995.50