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 $127.53   12.209%   $143.1001   $143.10   $143.10   $143.10  
  Purchase #2 $69.47   10.365%   $76.6706   $76.67   $76.65   $76.70  
  Purchase #3 $28.52   4.835%   $29.8989   $29.90   $29.90   $29.90  
  Purchase #4 $225.68   12.696%   $254.3323   $254.33   $254.35   $254.30  
  Purchase #5 $124.74   6.852%   $133.2872   $133.29   $133.30   $133.30  
  Purchase #6 $222.31   3.461%   $230.0041   $230.00   $230.00   $230.00  
  Purchase #7 $161.27   5.166%   $169.6012   $169.60   $169.60   $169.60  
  7 purchase totals = $959.52       $1,036.8944   $1,036.89   $1,036.90   $1,036.90