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 $165.79   5.863%   $175.5103   $175.51   $175.50   $175.50  
  Purchase #2 $178.52   5.871%   $189.0009   $189.00   $189.00   $189.00  
  Purchase #3 $92.81   6.192%   $98.5568   $98.56   $98.55   $98.60  
  Purchase #4 $232.55   6.423%   $247.4867   $247.49   $247.50   $247.50  
  Purchase #5 $228.29   11.336%   $254.169   $254.17   $254.15   $254.20  
  Purchase #6 $122.39   9.397%   $133.891   $133.89   $133.90   $133.90  
  Purchase #7 $220.72   12.289%   $247.8443   $247.84   $247.85   $247.80  
  7 purchase totals = $1,241.07       $1,346.4590   $1,346.46   $1,346.45   $1,346.50