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 $69.33   6.709%   $73.9813   $73.98   $74.00   $74.00  
  Purchase #2 $223.52   8.844%   $243.2881   $243.29   $243.30   $243.30  
  Purchase #3 $55.51   4.337%   $57.9175   $57.92   $57.90   $57.90  
  Purchase #4 $54.74   11.343%   $60.9492   $60.95   $60.95   $60.90  
  Purchase #5 $51.41   9.792%   $56.4441   $56.44   $56.45   $56.40  
  Purchase #6 $101.46   8.479%   $110.0628   $110.06   $110.05   $110.10  
  Purchase #7 $55.25   3.561%   $57.2175   $57.22   $57.20   $57.20  
  7 purchase totals = $611.22       $659.8605   $659.86   $659.85   $659.80