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 $161.51   13.323%   $183.028   $183.03   $183.05   $183.00  
  Purchase #2 $209.32   10.847%   $232.0249   $232.02   $232.00   $232.00  
  Purchase #3 $222.59   6.784%   $237.6905   $237.69   $237.70   $237.70  
  Purchase #4 $139.77   7.269%   $149.9299   $149.93   $149.95   $149.90  
  Purchase #5 $151.58   8.109%   $163.8716   $163.87   $163.85   $163.90  
  Purchase #6 $61.28   8.588%   $66.5427   $66.54   $66.55   $66.50  
  Purchase #7 $160.60   6.751%   $171.4421   $171.44   $171.45   $171.40  
  7 purchase totals = $1,106.65       $1,204.5297   $1,204.52   $1,204.55   $1,204.40