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 $62.85   4.117%   $65.4375   $65.44   $65.45   $65.40  
  Purchase #2 $234.58   3.870%   $243.6582   $243.66   $243.65   $243.70  
  Purchase #3 $222.59   10.748%   $246.514   $246.51   $246.50   $246.50  
  Purchase #4 $237.98   9.382%   $260.3073   $260.31   $260.30   $260.30  
  Purchase #5 $159.96   13.418%   $181.4234   $181.42   $181.40   $181.40  
  Purchase #6 $86.52   9.846%   $95.0388   $95.04   $95.05   $95.00  
  Purchase #7 $89.52   6.619%   $95.4453   $95.45   $95.45   $95.40  
  7 purchase totals = $1,094.00       $1,187.8245   $1,187.83   $1,187.80   $1,187.70