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 $76.35   11.831%   $85.383   $85.38   $85.40   $85.40  
  Purchase #2 $25.28   11.732%   $28.2458   $28.25   $28.25   $28.20  
  Purchase #3 $194.64   4.555%   $203.5059   $203.51   $203.50   $203.50  
  Purchase #4 $61.41   13.867%   $69.9257   $69.93   $69.95   $69.90  
  Purchase #5 $217.96   6.609%   $232.365   $232.37   $232.35   $232.40  
  Purchase #6 $27.85   5.865%   $29.4834   $29.48   $29.50   $29.50  
  Purchase #7 $211.57   5.229%   $222.633   $222.63   $222.65   $222.60  
  7 purchase totals = $815.06       $871.5418   $871.55   $871.60   $871.50