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 $214.66   6.370%   $228.3338   $228.33   $228.35   $228.30  
  Purchase #2 $165.81   7.138%   $177.6455   $177.65   $177.65   $177.60  
  Purchase #3 $85.33   5.864%   $90.3338   $90.33   $90.35   $90.30  
  Purchase #4 $29.41   6.833%   $31.4196   $31.42   $31.40   $31.40  
  Purchase #5 $61.72   3.120%   $63.6457   $63.65   $63.65   $63.60  
  Purchase #6 $200.60   8.782%   $218.2167   $218.22   $218.20   $218.20  
  Purchase #7 $200.62   5.555%   $211.7644   $211.76   $211.75   $211.80  
  7 purchase totals = $958.15       $1,021.3595   $1,021.36   $1,021.35   $1,021.20