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 $14.91   11.182%   $16.5772   $16.58   $16.60   $16.60  
  Purchase #2 $77.77   7.692%   $83.7521   $83.75   $83.75   $83.80  
  Purchase #3 $154.77   12.383%   $173.9352   $173.94   $173.95   $173.90  
  Purchase #4 $169.76   6.488%   $180.774   $180.77   $180.75   $180.80  
  Purchase #5 $165.76   9.804%   $182.0111   $182.01   $182.00   $182.00  
  Purchase #6 $107.49   11.203%   $119.5321   $119.53   $119.55   $119.50  
  Purchase #7 $235.31   10.376%   $259.7258   $259.73   $259.75   $259.70  
  7 purchase totals = $925.77       $1,016.3075   $1,016.31   $1,016.35   $1,016.30