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 $152.36   9.561%   $166.9271   $166.93   $166.95   $166.90  
  Purchase #2 $228.76   6.493%   $243.6134   $243.61   $243.60   $243.60  
  Purchase #3 $236.49   7.397%   $253.9832   $253.98   $254.00   $254.00  
  Purchase #4 $204.43   10.758%   $226.4226   $226.42   $226.40   $226.40  
  Purchase #5 $50.93   11.253%   $56.6612   $56.66   $56.65   $56.70  
  Purchase #6 $18.52   6.444%   $19.7134   $19.71   $19.70   $19.70  
  Purchase #7 $78.51   13.553%   $89.1505   $89.15   $89.15   $89.20  
  7 purchase totals = $970.00       $1,056.4714   $1,056.46   $1,056.45   $1,056.50