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 $231.46   9.326%   $253.046   $253.05   $253.05   $253.00  
  Purchase #2 $150.65   4.841%   $157.943   $157.94   $157.95   $157.90  
  Purchase #3 $22.50   3.854%   $23.3672   $23.37   $23.35   $23.40  
  Purchase #4 $158.70   11.124%   $176.3538   $176.35   $176.35   $176.40  
  Purchase #5 $215.25   11.596%   $240.2104   $240.21   $240.20   $240.20  
  Purchase #6 $119.26   6.419%   $126.9153   $126.92   $126.90   $126.90  
  Purchase #7 $50.84   3.613%   $52.6768   $52.68   $52.70   $52.70  
  7 purchase totals = $948.66       $1,030.5125   $1,030.52   $1,030.50   $1,030.50