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 $65.27   12.164%   $73.2094   $73.21   $73.20   $73.20  
  Purchase #2 $213.95   4.459%   $223.49   $223.49   $223.50   $223.50  
  Purchase #3 $245.55   4.430%   $256.4279   $256.43   $256.45   $256.40  
  Purchase #4 $119.44   4.601%   $124.9354   $124.94   $124.95   $124.90  
  Purchase #5 $35.52   11.735%   $39.6883   $39.69   $39.70   $39.70  
  Purchase #6 $133.56   10.716%   $147.8723   $147.87   $147.85   $147.90  
  Purchase #7 $208.66   10.519%   $230.6089   $230.61   $230.60   $230.60  
  7 purchase totals = $1,021.95       $1,096.2322   $1,096.24   $1,096.25   $1,096.20