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 $221.42   10.611%   $244.9149   $244.91   $244.90   $244.90  
  Purchase #2 $196.40   4.486%   $205.2105   $205.21   $205.20   $205.20  
  Purchase #3 $102.55   6.827%   $109.5511   $109.55   $109.55   $109.60  
  Purchase #4 $180.60   11.799%   $201.909   $201.91   $201.90   $201.90  
  Purchase #5 $71.52   3.423%   $73.9681   $73.97   $73.95   $74.00  
  Purchase #6 $179.28   11.544%   $199.9761   $199.98   $200.00   $200.00  
  Purchase #7 $213.64   10.236%   $235.5082   $235.51   $235.50   $235.50  
  7 purchase totals = $1,165.41       $1,271.0379   $1,271.04   $1,271.00   $1,271.10