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 $73.27   5.572%   $77.3526   $77.35   $77.35   $77.40  
  Purchase #2 $76.35   12.252%   $85.7044   $85.70   $85.70   $85.70  
  Purchase #3 $220.80   6.868%   $235.9645   $235.96   $235.95   $236.00  
  Purchase #4 $166.62   4.185%   $173.593   $173.59   $173.60   $173.60  
  Purchase #5 $165.80   13.277%   $187.8133   $187.81   $187.80   $187.80  
  Purchase #6 $58.45   5.220%   $61.5011   $61.50   $61.50   $61.50  
  Purchase #7 $6.39   9.818%   $7.0174   $7.02   $7.00   $7.00  
  7 purchase totals = $767.68       $828.9463   $828.93   $828.90   $829.00