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 $151.53   10.811%   $167.9119   $167.91   $167.90   $167.90  
  Purchase #2 $174.36   11.835%   $194.9955   $195.00   $195.00   $195.00  
  Purchase #3 $165.87   8.449%   $179.8844   $179.88   $179.90   $179.90  
  Purchase #4 $119.76   11.550%   $133.5923   $133.59   $133.60   $133.60  
  Purchase #5 $74.52   13.433%   $84.5303   $84.53   $84.55   $84.50  
  Purchase #6 $85.99   6.838%   $91.87   $91.87   $91.85   $91.90  
  Purchase #7 $220.45   3.383%   $227.9078   $227.91   $227.90   $227.90  
  7 purchase totals = $992.48       $1,080.6922   $1,080.69   $1,080.70   $1,080.70