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 $61.75   8.521%   $67.0117   $67.01   $67.00   $67.00  
  Purchase #2 $83.25   11.372%   $92.7172   $92.72   $92.70   $92.70  
  Purchase #3 $72.67   13.630%   $82.5749   $82.57   $82.55   $82.60  
  Purchase #4 $204.36   9.538%   $223.8519   $223.85   $223.85   $223.90  
  Purchase #5 $198.53   13.458%   $225.2482   $225.25   $225.25   $225.20  
  Purchase #6 $183.77   6.112%   $195.002   $195.00   $195.00   $195.00  
  Purchase #7 $39.33   11.800%   $43.9709   $43.97   $43.95   $44.00  
  7 purchase totals = $843.66       $930.3768   $930.37   $930.30   $930.40