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 $245.43   8.241%   $265.6559   $265.66   $265.65   $265.70  
  Purchase #2 $188.54   4.731%   $197.4598   $197.46   $197.45   $197.50  
  Purchase #3 $155.75   12.268%   $174.8574   $174.86   $174.85   $174.90  
  Purchase #4 $99.95   4.543%   $104.4907   $104.49   $104.50   $104.50  
  Purchase #5 $6.95   5.788%   $7.3523   $7.35   $7.35   $7.40  
  Purchase #6 $204.40   12.266%   $229.4717   $229.47   $229.45   $229.50  
  Purchase #7 $220.50   5.577%   $232.7973   $232.80   $232.80   $232.80  
  7 purchase totals = $1,121.52       $1,212.0851   $1,212.09   $1,212.05   $1,212.30