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 $237.94   12.203%   $266.9758   $266.98   $267.00   $267.00  
  Purchase #2 $212.90   13.173%   $240.9453   $240.95   $240.95   $240.90  
  Purchase #3 $124.71   9.718%   $136.8293   $136.83   $136.85   $136.80  
  Purchase #4 $30.83   6.405%   $32.8047   $32.80   $32.80   $32.80  
  Purchase #5 $200.58   9.810%   $220.2569   $220.26   $220.25   $220.30  
  Purchase #6 $179.52   8.232%   $194.2981   $194.30   $194.30   $194.30  
  Purchase #7 $242.83   8.343%   $263.0893   $263.09   $263.10   $263.10  
  7 purchase totals = $1,229.31       $1,355.1994   $1,355.21   $1,355.25   $1,355.20