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 $108.67   12.448%   $122.1972   $122.20   $122.20   $122.20  
  Purchase #2 $136.66   8.823%   $148.7175   $148.72   $148.70   $148.70  
  Purchase #3 $196.77   3.672%   $203.9954   $204.00   $204.00   $204.00  
  Purchase #4 $233.98   7.131%   $250.6651   $250.67   $250.65   $250.70  
  Purchase #5 $139.60   11.626%   $155.8299   $155.83   $155.85   $155.80  
  Purchase #6 $106.37   8.679%   $115.6019   $115.60   $115.60   $115.60  
  Purchase #7 $50.85   13.363%   $57.6451   $57.65   $57.65   $57.60  
  7 purchase totals = $972.90       $1,054.6521   $1,054.67   $1,054.65   $1,054.60