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 $217.38   13.477%   $246.6763   $246.68   $246.70   $246.70  
  Purchase #2 $191.99   10.592%   $212.3256   $212.33   $212.35   $212.30  
  Purchase #3 $17.66   11.359%   $19.666   $19.67   $19.65   $19.70  
  Purchase #4 $186.76   9.229%   $203.9961   $204.00   $204.00   $204.00  
  Purchase #5 $73.58   12.401%   $82.7047   $82.70   $82.70   $82.70  
  Purchase #6 $63.50   6.550%   $67.6593   $67.66   $67.65   $67.70  
  Purchase #7 $86.99   9.247%   $95.034   $95.03   $95.05   $95.00  
  7 purchase totals = $837.86       $928.0620   $928.07   $928.10   $928.10