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 $246.92   6.683%   $263.4217   $263.42   $263.40   $263.40  
  Purchase #2 $187.36   9.292%   $204.7695   $204.77   $204.75   $204.80  
  Purchase #3 $141.96   5.689%   $150.0361   $150.04   $150.05   $150.00  
  Purchase #4 $174.50   8.161%   $188.7409   $188.74   $188.75   $188.70  
  Purchase #5 $230.95   6.377%   $245.6777   $245.68   $245.70   $245.70  
  Purchase #6 $116.81   11.688%   $130.4628   $130.46   $130.45   $130.50  
  Purchase #7 $24.96   3.102%   $25.7343   $25.73   $25.75   $25.70  
  7 purchase totals = $1,123.46       $1,208.8430   $1,208.84   $1,208.85   $1,208.80