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 $118.93   13.145%   $134.5633   $134.56   $134.55   $134.60  
  Purchase #2 $248.71   4.244%   $259.2653   $259.27   $259.25   $259.30  
  Purchase #3 $8.64   10.237%   $9.5245   $9.52   $9.50   $9.50  
  Purchase #4 $204.26   12.778%   $230.3603   $230.36   $230.35   $230.40  
  Purchase #5 $156.96   12.467%   $176.5282   $176.53   $176.55   $176.50  
  Purchase #6 $144.60   3.675%   $149.9141   $149.91   $149.90   $149.90  
  Purchase #7 $58.31   3.258%   $60.2097   $60.21   $60.20   $60.20  
  7 purchase totals = $940.41       $1,020.3654   $1,020.36   $1,020.30   $1,020.40