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 $61.94   12.558%   $69.7184   $69.72   $69.70   $69.70  
  Purchase #2 $248.97   9.671%   $273.0479   $273.05   $273.05   $273.00  
  Purchase #3 $95.59   7.524%   $102.7822   $102.78   $102.80   $102.80  
  Purchase #4 $158.45   13.555%   $179.9279   $179.93   $179.95   $179.90  
  Purchase #5 $154.68   6.560%   $164.827   $164.83   $164.85   $164.80  
  Purchase #6 $191.62   10.197%   $211.1595   $211.16   $211.15   $211.20  
  Purchase #7 $84.58   7.464%   $90.8931   $90.89   $90.90   $90.90  
  7 purchase totals = $995.83       $1,092.3560   $1,092.36   $1,092.40   $1,092.30