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 $126.65   5.230%   $133.2738   $133.27   $133.25   $133.30  
  Purchase #2 $239.98   12.485%   $269.9415   $269.94   $269.95   $269.90  
  Purchase #3 $244.71   5.823%   $258.9595   $258.96   $258.95   $259.00  
  Purchase #4 $184.85   7.541%   $198.7895   $198.79   $198.80   $198.80  
  Purchase #5 $99.50   9.207%   $108.661   $108.66   $108.65   $108.70  
  Purchase #6 $139.29   9.245%   $152.1674   $152.17   $152.15   $152.20  
  Purchase #7 $115.75   7.574%   $124.5169   $124.52   $124.50   $124.50  
  7 purchase totals = $1,150.73       $1,246.3096   $1,246.31   $1,246.25   $1,246.40