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 $226.98   3.543%   $235.0219   $235.02   $235.00   $235.00  
  Purchase #2 $41.36   7.495%   $44.4599   $44.46   $44.45   $44.50  
  Purchase #3 $130.62   11.737%   $145.9509   $145.95   $145.95   $146.00  
  Purchase #4 $210.74   5.544%   $222.4234   $222.42   $222.40   $222.40  
  Purchase #5 $218.80   3.308%   $226.0379   $226.04   $226.05   $226.00  
  Purchase #6 $167.72   4.678%   $175.5659   $175.57   $175.55   $175.60  
  Purchase #7 $93.94   10.645%   $103.9399   $103.94   $103.95   $103.90  
  7 purchase totals = $1,090.16       $1,153.3998   $1,153.40   $1,153.35   $1,153.40