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 $136.52   6.871%   $145.9003   $145.90   $145.90   $145.90  
  Purchase #2 $214.50   13.416%   $243.2773   $243.28   $243.30   $243.30  
  Purchase #3 $32.52   13.618%   $36.9486   $36.95   $36.95   $36.90  
  Purchase #4 $112.61   11.835%   $125.9374   $125.94   $125.95   $125.90  
  Purchase #5 $91.92   11.228%   $102.2408   $102.24   $102.25   $102.20  
  Purchase #6 $97.54   12.722%   $109.949   $109.95   $109.95   $109.90  
  Purchase #7 $244.47   3.353%   $252.6671   $252.67   $252.65   $252.70  
  7 purchase totals = $930.08       $1,016.9205   $1,016.93   $1,016.95   $1,016.80