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 $89.52   8.151%   $96.8168   $96.82   $96.80   $96.80  
  Purchase #2 $126.80   5.836%   $134.2   $134.20   $134.20   $134.20  
  Purchase #3 $40.52   10.798%   $44.8953   $44.90   $44.90   $44.90  
  Purchase #4 $182.49   5.837%   $193.1419   $193.14   $193.15   $193.10  
  Purchase #5 $163.36   8.324%   $176.9581   $176.96   $176.95   $177.00  
  Purchase #6 $245.68   7.267%   $263.5336   $263.53   $263.55   $263.50  
  Purchase #7 $64.53   12.751%   $72.7582   $72.76   $72.75   $72.80  
  7 purchase totals = $912.90       $982.3039   $982.31   $982.30   $982.30