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 $119.41   12.658%   $134.5249   $134.52   $134.50   $134.50  
  Purchase #2 $109.88   12.523%   $123.6403   $123.64   $123.65   $123.60  
  Purchase #3 $243.28   7.740%   $262.1099   $262.11   $262.10   $262.10  
  Purchase #4 $22.98   5.390%   $24.2186   $24.22   $24.20   $24.20  
  Purchase #5 $208.61   7.735%   $224.746   $224.75   $224.75   $224.70  
  Purchase #6 $163.95   7.530%   $176.2954   $176.30   $176.30   $176.30  
  Purchase #7 $214.80   3.689%   $222.724   $222.72   $222.70   $222.70  
  7 purchase totals = $1,082.91       $1,168.2591   $1,168.26   $1,168.20   $1,168.10