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 $181.69   12.391%   $204.2032   $204.20   $204.20   $204.20  
  Purchase #2 $137.31   10.481%   $151.7015   $151.70   $151.70   $151.70  
  Purchase #3 $73.80   8.873%   $80.3483   $80.35   $80.35   $80.30  
  Purchase #4 $68.88   8.762%   $74.9153   $74.92   $74.90   $74.90  
  Purchase #5 $34.51   8.721%   $37.5196   $37.52   $37.50   $37.50  
  Purchase #6 $5.62   10.351%   $6.2017   $6.20   $6.20   $6.20  
  Purchase #7 $193.37   7.494%   $207.8611   $207.86   $207.85   $207.90  
  7 purchase totals = $695.18       $762.7507   $762.75   $762.70   $762.70