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 $70.46   11.664%   $78.6785   $78.68   $78.70   $78.70  
  Purchase #2 $164.82   8.776%   $179.2846   $179.28   $179.30   $179.30  
  Purchase #3 $131.63   9.712%   $144.4139   $144.41   $144.40   $144.40  
  Purchase #4 $61.69   8.721%   $67.07   $67.07   $67.05   $67.10  
  Purchase #5 $62.52   4.290%   $65.2021   $65.20   $65.20   $65.20  
  Purchase #6 $87.95   8.776%   $95.6685   $95.67   $95.65   $95.70  
  Purchase #7 $218.46   5.596%   $230.685   $230.69   $230.70   $230.70  
  7 purchase totals = $797.53       $861.0026   $861.00   $861.00   $861.10