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 $244.98   6.233%   $260.2496   $260.25   $260.25   $260.20  
  Purchase #2 $181.79   6.836%   $194.2172   $194.22   $194.20   $194.20  
  Purchase #3 $186.61   8.845%   $203.1157   $203.12   $203.10   $203.10  
  Purchase #4 $131.85   3.687%   $136.7113   $136.71   $136.70   $136.70  
  Purchase #5 $34.39   9.474%   $37.6481   $37.65   $37.65   $37.60  
  Purchase #6 $118.57   10.706%   $131.2641   $131.26   $131.25   $131.30  
  Purchase #7 $94.89   12.803%   $107.0388   $107.04   $107.05   $107.00  
  7 purchase totals = $993.08       $1,070.2448   $1,070.25   $1,070.20   $1,070.10