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 $38.79   13.167%   $43.8975   $43.90   $43.90   $43.90  
  Purchase #2 $60.87   8.367%   $65.963   $65.96   $65.95   $66.00  
  Purchase #3 $44.39   10.350%   $48.9844   $48.98   $49.00   $49.00  
  Purchase #4 $196.87   13.184%   $222.8253   $222.83   $222.85   $222.80  
  Purchase #5 $223.29   7.335%   $239.6683   $239.67   $239.65   $239.70  
  Purchase #6 $198.54   7.836%   $214.0976   $214.10   $214.10   $214.10  
  Purchase #7 $244.86   3.355%   $253.0751   $253.08   $253.10   $253.10  
  7 purchase totals = $1,007.61       $1,088.5112   $1,088.52   $1,088.55   $1,088.60