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 $76.54   11.861%   $85.6184   $85.62   $85.60   $85.60  
  Purchase #2 $187.59   13.815%   $213.5056   $213.51   $213.50   $213.50  
  Purchase #3 $119.96   13.285%   $135.8967   $135.90   $135.90   $135.90  
  Purchase #4 $153.73   11.669%   $171.6688   $171.67   $171.65   $171.70  
  Purchase #5 $188.75   6.858%   $201.6945   $201.69   $201.70   $201.70  
  Purchase #6 $96.45   6.379%   $102.6025   $102.60   $102.60   $102.60  
  Purchase #7 $60.65   8.148%   $65.5918   $65.59   $65.60   $65.60  
  7 purchase totals = $883.67       $976.5783   $976.58   $976.55   $976.60