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 $119.57   6.215%   $127.0013   $127.00   $127.00   $127.00  
  Purchase #2 $94.65   9.238%   $103.3938   $103.39   $103.40   $103.40  
  Purchase #3 $248.52   8.774%   $270.3251   $270.33   $270.35   $270.30  
  Purchase #4 $191.87   9.719%   $210.5178   $210.52   $210.50   $210.50  
  Purchase #5 $48.36   5.807%   $51.1683   $51.17   $51.15   $51.20  
  Purchase #6 $115.50   12.486%   $129.9213   $129.92   $129.90   $129.90  
  Purchase #7 $198.31   12.781%   $223.656   $223.66   $223.65   $223.70  
  7 purchase totals = $1,016.78       $1,115.9836   $1,115.99   $1,115.95   $1,116.00