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 $216.91   11.127%   $241.0456   $241.05   $241.05   $241.00  
  Purchase #2 $166.50   6.689%   $177.6372   $177.64   $177.65   $177.60  
  Purchase #3 $185.48   10.564%   $205.0741   $205.07   $205.05   $205.10  
  Purchase #4 $88.45   4.362%   $92.3082   $92.31   $92.30   $92.30  
  Purchase #5 $188.40   6.236%   $200.1486   $200.15   $200.15   $200.10  
  Purchase #6 $68.57   6.514%   $73.0366   $73.04   $73.05   $73.00  
  Purchase #7 $170.34   4.601%   $178.1773   $178.18   $178.20   $178.20  
  7 purchase totals = $1,084.65       $1,167.4276   $1,167.44   $1,167.45   $1,167.30