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 $247.93   7.367%   $266.195   $266.20   $266.20   $266.20  
  Purchase #2 $128.45   11.357%   $143.0381   $143.04   $143.05   $143.00  
  Purchase #3 $106.47   4.585%   $111.3516   $111.35   $111.35   $111.40  
  Purchase #4 $239.56   8.496%   $259.913   $259.91   $259.90   $259.90  
  Purchase #5 $203.96   5.192%   $214.5496   $214.55   $214.55   $214.50  
  Purchase #6 $77.53   10.874%   $85.9606   $85.96   $85.95   $86.00  
  Purchase #7 $138.53   8.873%   $150.8218   $150.82   $150.80   $150.80  
  7 purchase totals = $1,142.43       $1,231.8297   $1,231.83   $1,231.80   $1,231.80