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 $106.82   10.631%   $118.176   $118.18   $118.20   $118.20  
  Purchase #2 $177.60   6.563%   $189.2559   $189.26   $189.25   $189.30  
  Purchase #3 $28.72   13.574%   $32.6185   $32.62   $32.60   $32.60  
  Purchase #4 $53.59   13.816%   $60.994   $60.99   $61.00   $61.00  
  Purchase #5 $43.25   6.239%   $45.9484   $45.95   $45.95   $45.90  
  Purchase #6 $204.77   11.762%   $228.855   $228.86   $228.85   $228.90  
  Purchase #7 $151.42   3.314%   $156.4381   $156.44   $156.45   $156.40  
  7 purchase totals = $766.17       $832.2859   $832.30   $832.30   $832.30