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 $140.30   9.515%   $153.6495   $153.65   $153.65   $153.60  
  Purchase #2 $240.73   9.641%   $263.9388   $263.94   $263.95   $263.90  
  Purchase #3 $136.27   11.193%   $151.5227   $151.52   $151.50   $151.50  
  Purchase #4 $93.79   9.549%   $102.746   $102.75   $102.75   $102.70  
  Purchase #5 $209.49   7.599%   $225.4091   $225.41   $225.40   $225.40  
  Purchase #6 $105.65   5.770%   $111.746   $111.75   $111.75   $111.70  
  Purchase #7 $222.83   5.853%   $235.8722   $235.87   $235.85   $235.90  
  7 purchase totals = $1,149.06       $1,244.8843   $1,244.89   $1,244.85   $1,244.70