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 $202.27   7.789%   $218.0248   $218.02   $218.00   $218.00  
  Purchase #2 $75.56   4.614%   $79.0463   $79.05   $79.05   $79.00  
  Purchase #3 $224.81   7.454%   $241.5673   $241.57   $241.55   $241.60  
  Purchase #4 $185.30   9.789%   $203.439   $203.44   $203.45   $203.40  
  Purchase #5 $127.82   5.152%   $134.4053   $134.41   $134.40   $134.40  
  Purchase #6 $193.85   6.243%   $205.9521   $205.95   $205.95   $206.00  
  Purchase #7 $157.37   12.841%   $177.5779   $177.58   $177.60   $177.60  
  7 purchase totals = $1,166.98       $1,260.0127   $1,260.02   $1,260.00   $1,260.00